Merge the tonic layer from skydart branch back to master

sky/engine/tonic/dart_value.h

Index: sky/engine/tonic/dart_value.h
diff --git a/sky/engine/tonic/dart_value.h b/sky/engine/tonic/dart_value.h
new file mode 100644
index 0000000000000000000000000000000000000000..57332e451b1f0ff110b430f82e114b3738b53773
--- /dev/null
+++ b/sky/engine/tonic/dart_value.h
@@ -0,0 +1,59 @@
+// 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.
+
+#ifndef SKY_ENGINE_TONIC_DART_VALUE_H_
+#define SKY_ENGINE_TONIC_DART_VALUE_H_
+
+#include "base/logging.h"
+#include "dart/runtime/include/dart_api.h"
+#include "sky/engine/tonic/dart_persistent_value.h"
+#include "sky/engine/tonic/dart_state.h"
+#include "sky/engine/wtf/RefPtr.h"
+
+namespace blink {
+
+// DartValue is a convience wrapper around DartPersistentValue that lets clients
+// use RefPtr to keep track of the number of references to the underlying Dart
+// object. Be careful when retaining RefPtr<DartValue> in the heap because the
+// VM's garbage collector cannot break cycles that involve the C++ heap, which
+// can lead to memory leaks.
+class DartValue : public RefCounted<DartValue> {
+ public:
+  static PassRefPtr<DartValue> Create(DartState* dart_state,
+                                      Dart_Handle value) {
+    return adoptRef(new DartValue(dart_state, value));
+  }
+
+  static PassRefPtr<DartValue> Create() { return adoptRef(new DartValue()); }
+
+  ~DartValue();
+
+  Dart_Handle dart_value() const { return dart_value_.value(); }
+  bool is_empty() const { return !dart_value(); }
+
+  bool is_null() const {
+    DCHECK(!is_empty());
+    return Dart_IsNull(dart_value());
+  }
+
+  bool is_function() const {
+    DCHECK(!is_empty());
+    return Dart_IsClosure(dart_value());
+  }
+
+  bool Equals(DartValue* other) const;
+  void Clear();
+
+ private:
+  DartValue();
+  DartValue(DartState* dart_state, Dart_Handle value);
+
+  DartPersistentValue dart_value_;
+
+  DISALLOW_COPY_AND_ASSIGN(DartValue);
+};
+
+}  // namespace blink
+
+#endif  // SKY_ENGINE_TONIC_DART_VALUE_H_