Add File.lengthSync to use it for FileByteStore eviction.

R=brianwilkerson@google.com, paulberry@google.com
BUG=

Review URL: https://codereview.chromium.org/2490023003 .

pkg/analyzer/lib/file_system/file_system.dart

@@ -20,9 +20,15 @@ abstract class File implements Resource {
    */
   Stream<WatchEvent> get changes;
 
+  /**
+   * Synchronously get the length of the file.
+   * Throws a [FileSystemException] if the operation fails.
+   */
+  int get lengthSync;
+
   /**
    * Return the last-modified stamp of the file.
-   * Throws [FileSystemException] if the file does not exist.
+   * Throws a [FileSystemException] if the file does not exist.
    */
   int get modificationStamp;
 

pkg/analyzer/lib/file_system/memory_file_system.dart

@@ -305,6 +305,11 @@ class _MemoryDummyLink extends _MemoryResource implements File {
   @override
   bool get exists => false;
 
+  @override
+  int get lengthSync {
+    throw new FileSystemException(path, 'File could not be read');
+  }
+
   @override
   int get modificationStamp {
     int stamp = _provider._pathToTimestamp[path];
@@ -370,6 +375,11 @@ class _MemoryFile extends _MemoryResource implements File {
   @override
   bool get exists => _provider._pathToResource[path] is _MemoryFile;
 
+  @override
+  int get lengthSync {
+    return readAsBytesSync().length;
+  }
+
   @override
   int get modificationStamp {
     int stamp = _provider._pathToTimestamp[path];

pkg/analyzer/lib/file_system/physical_file_system.dart

@@ -126,6 +126,15 @@ class _PhysicalFile extends _PhysicalResource implements File {
   @override
   Stream<WatchEvent> get changes => new FileWatcher(_entry.path).events;
 
+  @override
+  int get lengthSync {
+    try {
+      return _file.lengthSync();
+    } on io.FileSystemException catch (exception) {
+      throw new FileSystemException(exception.path, exception.message);
+    }
+  }
+
   @override
   int get modificationStamp {
     try {

pkg/analyzer/test/file_system/memory_file_system_test.dart

@@ -111,6 +111,20 @@ class FileTest {
     expect(file.isOrContains(provider.convertPath('/foo/bar')), isFalse);
   }
 
+  void test_lengthSync_doesNotExist() {
+    File file = provider.getResource(provider.convertPath('/test.txt'));
+    expect(() {
+      file.lengthSync;
+    }, throwsA(_isFileSystemException));
+  }
+
+  void test_lengthSync_exists() {
+    List<int> bytes = <int>[1, 2, 3, 4, 5];
+    File file =
+        provider.newFileWithBytes(provider.convertPath('/file.bin'), bytes);
+    expect(file.lengthSync, bytes.length);
+  }
+
   void test_modificationStamp_doesNotExist() {
     String path = provider.convertPath('/foo/bar/file.txt');
     File file = provider.newFile(path, 'qwerty');

pkg/analyzer/test/file_system/physical_resource_provider_test.dart

@@ -97,6 +97,19 @@ class FileTest extends _BaseTest {
     expect(file.isOrContains('foo'), isFalse);
   }
 
+  void test_lengthSync_doesNotExist() {
+    File file = PhysicalResourceProvider.INSTANCE.getResource(path);
+    expect(() {
+      file.lengthSync;
+    }, throwsA(_isFileSystemException));
+  }
+
+  void test_lengthSync_exists() {
+    List<int> bytes = <int>[1, 2, 3, 4, 5];
+    new io.File(path).writeAsBytesSync(bytes);
+    expect(file.lengthSync, bytes.length);
+  }
+
   void test_modificationStamp_doesNotExist() {
     File file = PhysicalResourceProvider.INSTANCE.getResource(path);
     expect(() {