Update comments in core lib showing proper factory syntax.

runtime/vm/dart_api_impl_test.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 
 #include "vm/assert.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_api_state.h"
 #include "vm/unit_test.h"
@@ skipping 1168 matching lines @@
 
     // Load up a test script in the test library.
     Dart_Handle lib = TestCase::LoadTestScript(kScriptChars, NULL);
 
     // Invoke a function which returns an object of type NativeFields.
     result = Dart_InvokeStatic(lib,
                                Dart_NewString("NativeFieldsTest"),
                                Dart_NewString("testMain"),
                                0,
                                NULL);
-    // We expect the test script to fail finalization with the error :
-    // "class 'NativeFields' is trying to extend a native fields class,"
-    // "but library 'TestCase::url()' has no native resolvers".
+    // We expect the test script to fail finalization with the error below:
     EXPECT(Dart_IsError(result));
     Dart_Handle expected_error = Dart_Error(
-        "class 'NativeFields' is trying to extend a native fields class,"
-        "but library '%s' has no native resolvers", TestCase::url());
+        "'dart:test-lib': Error: class 'NativeFields' is trying to extend a "
+        "native fields class, but library '%s' has no native resolvers",
+        TestCase::url());
     EXPECT_STREQ(Dart_GetError(expected_error), Dart_GetError(result));
     Dart_ExitScope();  // Exit the Dart API scope.
   }
   Dart_ShutdownIsolate();
 }
 
 
 static void TestNativeFields(Dart_Handle retobj) {
   // Access and set various instance fields of the object.
   Dart_Handle result = Dart_GetInstanceField(retobj, Dart_NewString("fld3"));
@@ skipping 1072 matching lines @@
                                NULL);
     EXPECT_VALID(result);
 
     Dart_ExitScope();  // Exit the Dart API scope.
   }
   Dart_ShutdownIsolate();
 }
 #endif  // TARGET_ARCH_IA32.
 
 }  // namespace dart