Remove most comment syntax casts from sdk.

Eliminates all of the uses of the "/*=" syntax in the sdk libraries
that can be trivially converted to implicit downcasts.

Bug:
Change-Id: I213a5d683f50d0cec0b32482f44330db3b5d618d
Reviewed-on: https://dart-review.googlesource.com/21781
Commit-Queue: Leaf Petersen <leafp@google.com>
Reviewed-by: Stephen Adams <sra@google.com>
Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>

sdk/lib/collection/hash_map.dart

@@ -104,7 +104,7 @@ abstract class HashMap<K, V> implements Map<K, V> {
   factory HashMap.from(Map other) {
     HashMap<K, V> result = new HashMap<K, V>();
     other.forEach((k, v) {
-      result[k as Object/*=K*/] = v as Object/*=V*/;
+      result[k] = v;
     });
     return result;
   }

sdk/lib/collection/hash_set.dart

@@ -129,8 +129,7 @@ abstract class HashSet<E> implements Set<E> {
   factory HashSet.from(Iterable elements) {
     HashSet<E> result = new HashSet<E>();
     for (final e in elements) {
-      E element = e as Object/*=E*/;
-      result.add(element);
+      result.add(e);
     }
     return result;
   }

sdk/lib/collection/linked_hash_map.dart

@@ -91,7 +91,7 @@ abstract class LinkedHashMap<K, V> implements HashMap<K, V> {
   factory LinkedHashMap.from(Map other) {
     LinkedHashMap<K, V> result = new LinkedHashMap<K, V>();
     other.forEach((k, v) {
-      result[k as Object/*=K*/] = v as Object/*=V*/;
+      result[k] = v;
     });
     return result;
   }

sdk/lib/collection/linked_hash_set.dart

@@ -106,8 +106,7 @@ abstract class LinkedHashSet<E> implements HashSet<E> {
   factory LinkedHashSet.from(Iterable elements) {
     LinkedHashSet<E> result = new LinkedHashSet<E>();
     for (final element in elements) {
-      E e = element as Object/*=E*/;
-      result.add(e);
+      result.add(element);
     }
     return result;
   }

sdk/lib/collection/linked_list.dart

@@ -288,6 +288,6 @@ abstract class LinkedListEntry<E extends LinkedListEntry<E>> {
    * The [entry] must not be in a linked list.
    */
   void insertBefore(E entry) {
-    _list._insertBefore(this as dynamic/*=E*/, entry, updateFirst: true);
+    _list._insertBefore(this, entry, updateFirst: true);
   }
 }

sdk/lib/collection/queue.dart

@@ -172,14 +172,12 @@ abstract class _DoubleLinkedQueueEntry<E> extends DoubleLinkedQueueEntry<E> {
   E get _element => element;
 
   DoubleLinkedQueueEntry<E> nextEntry() {
-    _DoubleLinkedQueueEntry<E> entry =
-        _nextLink as dynamic/*=DoubleLinkedQueueEntry<E>*/;
+    _DoubleLinkedQueueEntry<E> entry = _nextLink;
     return entry._asNonSentinelEntry();
   }
 
   DoubleLinkedQueueEntry<E> previousEntry() {
-    _DoubleLinkedQueueEntry<E> entry =
-        _previousLink as dynamic/*=DoubleLinkedQueueEntry<E>*/;
+    _DoubleLinkedQueueEntry<E> entry = _previousLink;
     return entry._asNonSentinelEntry();
   }
 }
@@ -271,8 +269,7 @@ class DoubleLinkedQueue<E> extends Iterable<E> implements Queue<E> {
   factory DoubleLinkedQueue.from(Iterable elements) {
     Queue<E> list = new DoubleLinkedQueue<E>();
     for (final e in elements) {
-      E element = e as Object/*=E*/;
-      list.addLast(element);
+      list.addLast(e);
     }
     return list;
   }
@@ -536,7 +533,7 @@ class ListQueue<E> extends ListIterable<E> implements Queue<E> {
       ListQueue<E> queue = new ListQueue<E>(length + 1);
       assert(queue._table.length > length);
       for (int i = 0; i < length; i++) {
-        queue._table[i] = elements[i] as Object/*=E*/;
+        queue._table[i] = elements[i];
       }
       queue._tail = length;
       return queue;
@@ -547,7 +544,7 @@ class ListQueue<E> extends ListIterable<E> implements Queue<E> {
       }
       ListQueue<E> result = new ListQueue<E>(capacity);
       for (final element in elements) {
-        result.addLast(element as Object/*=E*/);
+        result.addLast(element);
       }
       return result;
     }

sdk/lib/collection/splay_tree.dart

@@ -300,7 +300,7 @@ class SplayTreeMap<K, V> extends _SplayTree<K, _SplayTreeMapNode<K, V>>
       [int compare(K key1, K key2), bool isValidKey(potentialKey)]) {
     SplayTreeMap<K, V> result = new SplayTreeMap<K, V>(compare, isValidKey);
     other.forEach((k, v) {
-      result[k as Object/*=K*/] = v as Object/*=V*/;
+      result[k] = v;
     });
     return result;
   }
@@ -353,7 +353,7 @@ class SplayTreeMap<K, V> extends _SplayTree<K, _SplayTreeMapNode<K, V>>
   V operator [](Object key) {
     if (!_validKey(key)) return null;
     if (_root != null) {
-      int comp = _splay(key as dynamic/*=K*/);
+      int comp = _splay(key);
       if (comp == 0) {
         return _root.value;
       }
@@ -363,7 +363,7 @@ class SplayTreeMap<K, V> extends _SplayTree<K, _SplayTreeMapNode<K, V>>
 
   V remove(Object key) {
     if (!_validKey(key)) return null;
-    _SplayTreeMapNode<K, V> mapRoot = _remove(key as dynamic/*=K*/);
+    _SplayTreeMapNode<K, V> mapRoot = _remove(key);
     if (mapRoot != null) return mapRoot.value;
     return null;
   }
@@ -430,7 +430,7 @@ class SplayTreeMap<K, V> extends _SplayTree<K, _SplayTreeMapNode<K, V>>
   }
 
   bool containsKey(Object key) {
-    return _validKey(key) && _splay(key as dynamic/*=K*/) == 0;
+    return _validKey(key) && _splay(key) == 0;
   }
 
   bool containsValue(Object value) {
@@ -654,8 +654,7 @@ class _SplayTreeKeyIterator<K> extends _SplayTreeIterator<K, K> {
 class _SplayTreeValueIterator<K, V> extends _SplayTreeIterator<K, V> {
   _SplayTreeValueIterator(SplayTreeMap<K, V> map) : super(map);
   V _getValue(_SplayTreeNode<K> node) {
-    _SplayTreeMapNode<K, V> mapNode =
-        node as dynamic/*=_SplayTreeMapNode<K, V>*/;
+    _SplayTreeMapNode<K, V> mapNode = node;
     return mapNode.value;
   }
 }
@@ -732,7 +731,7 @@ class SplayTreeSet<E> extends _SplayTree<E, _SplayTreeNode<E>>
       [int compare(E key1, E key2), bool isValidKey(potentialKey)]) {
     SplayTreeSet<E> result = new SplayTreeSet<E>(compare, isValidKey);
     for (final element in elements) {
-      E e = element as Object/*=E*/;
+      E e = element;
       result.add(e);
     }
     return result;
@@ -766,7 +765,7 @@ class SplayTreeSet<E> extends _SplayTree<E, _SplayTreeNode<E>>
 
   // From Set.
   bool contains(Object element) {
-    return _validKey(element) && _splay(element as dynamic/*=E*/) == 0;
+    return _validKey(element) && _splay(element) == 0;
   }
 
   bool add(E element) {
@@ -778,7 +777,7 @@ class SplayTreeSet<E> extends _SplayTree<E, _SplayTreeNode<E>>
 
   bool remove(Object object) {
     if (!_validKey(object)) return false;
-    return _remove(object as dynamic/*=E*/) != null;
+    return _remove(object) != null;
   }
 
   void addAll(Iterable<E> elements) {
@@ -792,7 +791,7 @@ class SplayTreeSet<E> extends _SplayTree<E, _SplayTreeNode<E>>
 
   void removeAll(Iterable<Object> elements) {
     for (Object element in elements) {
-      if (_validKey(element)) _remove(element as dynamic/*=E*/);
+      if (_validKey(element)) _remove(element);
     }
   }
 
@@ -806,7 +805,7 @@ class SplayTreeSet<E> extends _SplayTree<E, _SplayTreeNode<E>>
         throw new ConcurrentModificationError(this);
       }
       // Equivalent to this.contains(object).
-      if (_validKey(object) && _splay(object as dynamic/*=E*/) == 0) {
+      if (_validKey(object) && _splay(object) == 0) {
         retainSet.add(_root.key);
       }
     }
@@ -820,7 +819,7 @@ class SplayTreeSet<E> extends _SplayTree<E, _SplayTreeNode<E>>
 
   E lookup(Object object) {
     if (!_validKey(object)) return null;
-    int comp = _splay(object as dynamic/*=E*/);
+    int comp = _splay(object);
     if (comp != 0) return null;
     return _root.key;
   }

sdk/lib/convert/json.dart

@@ -282,8 +282,11 @@ class JsonEncoder extends Converter<Object, String> {
 
   Converter<Object, T> fuse<T>(Converter<String, T> other) {
     if (other is Utf8Encoder) {
-      return new JsonUtf8Encoder(indent, _toEncodable)
-          as dynamic/*=Converter<Object, T>*/;
+      // The instance check guarantees that `T` is (a subtype of) List<int>,
+      // but the static type system doesn't know that, and so we cast.
+      // Cast through dynamic to keep the cast implicit for builds using
+      // unchecked implicit casts.
+      return new JsonUtf8Encoder(indent, _toEncodable) as dynamic;
     }
     return super.fuse<T>(other);
   }

sdk/lib/io/file_impl.dart

@@ -726,7 +726,8 @@ class _RandomAccessFile implements RandomAccessFile {
         throw _exceptionFromResponse(response, "read failed", path);
       }
       _resourceInfo.addRead(response[1].length);
-      return response[1] as Object/*=List<int>*/;
+      List<int> result = response[1];
+      return result;
     });
   }
 
@@ -740,7 +741,7 @@ class _RandomAccessFile implements RandomAccessFile {
       throw new FileSystemException("readSync failed", path, result);
     }
     _resourceInfo.addRead(result.length);
-    return result as Object/*=List<int>*/;
+    return result;
   }
 
   Future<int> readInto(List<int> buffer, [int start = 0, int end]) {
@@ -758,8 +759,8 @@ class _RandomAccessFile implements RandomAccessFile {
       if (_isErrorResponse(response)) {
         throw _exceptionFromResponse(response, "readInto failed", path);
       }
-      var read = response[1];
-      var data = response[2] as Object/*=List<int>*/;
+      int read = response[1];
+      List<int> data = response[2];
       buffer.setRange(start, start + read, data);
       _resourceInfo.addRead(read);
       return read;

sdk/lib/io/platform_impl.dart

@@ -116,7 +116,7 @@ class _Platform {
     if (_environmentCache is OSError) {
       throw _environmentCache;
     } else {
-      return _environmentCache as Object/*=Map<String, String>*/;
+      return _environmentCache;
     }
   }
 

sdk/lib/math/point.dart

@@ -58,8 +58,7 @@ class Point<T extends num> {
    * _runtime_ _error_ in checked mode.
    */
   Point<T> operator *(num /*T|int*/ factor) {
-    return new Point<T>(
-        (x * factor) as dynamic/*=T*/, (y * factor) as dynamic/*=T*/);
+    return new Point<T>((x * factor), (y * factor));
   }
 
   /**