Add Dart_Allocate to the C++ API

runtime/vm/dart_api_impl_test.cc

Index: runtime/vm/dart_api_impl_test.cc
diff --git a/runtime/vm/dart_api_impl_test.cc b/runtime/vm/dart_api_impl_test.cc
index 67b2f8a4167c8731fe15330258e0f4b967e95ef9..73d9b197c2b686566c5d314d25aac466f93c9410 100644
--- a/runtime/vm/dart_api_impl_test.cc
+++ b/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);

[siva, 2013/06/19 15:36:24]

I think you may run into conflicts with my CL. I have changed this
test to do a Dart_GetType above so that it uses type objects.

If you submit first I will resolve this conflict otherwise you may have to
resolve it.

+  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);