Add Dart_Allocate to the C++ API

This change allows us to allocate Dart objects from C++ without
invoking a constructor.  In turn, it allows us to declare Dartium DOM
types with no public generative constructor.

Note, the current constructor has to be public as dart:html Element is
subclassed by dart:svg SvgElement (and eventually by user defined
custom elements as well).  This leads to unfortunate holes such as: https://code.google.com/p/dart/issues/detail?id=11277

This should also give a modest boost in DOM perf as the existing
constructor does absolutely nothing.

BUG=11277
R=asiva@google.com

Review URL: https://codereview.chromium.org//16968006

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@24189 260f80e4-7a28-3924-810f-c04153c831b5

runtime/include/dart_api.h

@@ -1752,6 +1752,16 @@ DART_EXPORT Dart_Handle Dart_New(Dart_Handle clazz,
                                  int number_of_arguments,
                                  Dart_Handle* arguments);
 
+/**
+ * Allocate a new object without invoking a constructor.
+ *
+ * \param type The type of an object to be allocated.
+ *
+ * \return The new object. If an error occurs during execution, then an
+ *   error handle is returned.
+ */
+DART_EXPORT Dart_Handle Dart_Allocate(Dart_Handle type);
+
 /**
  * Invokes a method or function.
  *

runtime/vm/dart_api_impl.cc

@@ -2825,6 +2825,33 @@ DART_EXPORT Dart_Handle Dart_New(Dart_Handle clazz,
 }
 
 
+DART_EXPORT Dart_Handle Dart_Allocate(Dart_Handle type) {
+  Isolate* isolate = Isolate::Current();
+  DARTSCOPE(isolate);
+  CHECK_CALLBACK_STATE(isolate);
+  const Object& result = Object::Handle(isolate, Api::UnwrapHandle(type));
+
+  // Get the class to instantiate.
+  if (result.IsNull()) {
+    RETURN_TYPE_ERROR(isolate, type, Type);
+  }
+  Class& cls = Class::Handle(isolate);
+  if (result.IsType()) {
+    cls = Type::Cast(result).type_class();
+  } else if (result.IsClass()) {
+    // For backwards compatibility we allow class objects to be passed in
+    // for now. This needs to be removed once all code that uses class
+    // objects to invoke Dart_New is removed.
+    cls ^= result.raw();
+  } else {
+    RETURN_TYPE_ERROR(isolate, type, Type);
+  }
+
+  // Allocate an object for the given class.
+  return Api::NewHandle(isolate, Instance::New(cls));
+}
+
+
 DART_EXPORT Dart_Handle Dart_Invoke(Dart_Handle target,
                                     Dart_Handle name,
                                     int number_of_arguments,

runtime/vm/dart_api_impl_test.cc

@@ -3919,6 +3919,15 @@ TEST_CASE(New) {
   EXPECT_VALID(Dart_IntegerToInt64(foo, &int_value));
   EXPECT_EQ(7, int_value);
 
+  // Allocate without a constructor.
+  result = Dart_Allocate(cls);
+  EXPECT_VALID(result);
+  instanceof = false;
+  EXPECT_VALID(Dart_ObjectIsType(result, cls, &instanceof));
+  EXPECT(instanceof);
+  foo = Dart_GetField(result, NewString("foo"));
+  EXPECT(Dart_IsNull(foo));
+
   // Invoke the unnamed constructor with an empty string.
   result = Dart_New(cls, NewString(""), 0, NULL);
   EXPECT_VALID(result);