Merge the tonic layer from skydart branch back to master

sky/engine/tonic/dart_value.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sky/engine/config.h"
+#include "sky/engine/tonic/dart_value.h"
+
+namespace blink {
+
+DartValue::DartValue() {
+}
+
+DartValue::DartValue(DartState* dart_state, Dart_Handle value)
+    : dart_value_(dart_state, value) {
+}
+
+DartValue::~DartValue() {
+}
+
+bool DartValue::Equals(DartValue* other) const {
+  DCHECK(other);
+  if (is_empty())
+    return other->is_empty();
+  if (other->is_empty())
+    return false;
+  return Dart_IdentityEquals(dart_value(), other->dart_value());
+}
+
+void DartValue::Clear() {
+  dart_value_.Clear();
+}
+
+}  // namespace blink