Merge the tonic layer from skydart branch back to master

sky/engine/tonic/dart_isolate_scope.h

Index: sky/engine/tonic/dart_isolate_scope.h
diff --git a/sky/engine/tonic/dart_isolate_scope.h b/sky/engine/tonic/dart_isolate_scope.h
new file mode 100644
index 0000000000000000000000000000000000000000..778fa8e6c3efcc8858d4a3e0f6e86a4ab1fee73a
--- /dev/null
+++ b/sky/engine/tonic/dart_isolate_scope.h
@@ -0,0 +1,28 @@
+// 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_ISOLATE_SCOPE_H_
+#define SKY_ENGINE_TONIC_DART_ISOLATE_SCOPE_H_
+
+#include "base/logging.h"
+#include "dart/runtime/include/dart_api.h"
+
+namespace blink {
+
+// DartIsolateScope is a helper class for entering and exiting a given isolate.
+class DartIsolateScope {
+ public:
+  explicit DartIsolateScope(Dart_Isolate isolate);
+  ~DartIsolateScope();
+
+ private:
+  Dart_Isolate isolate_;
+  Dart_Isolate previous_;
+
+  DISALLOW_COPY_AND_ASSIGN(DartIsolateScope);
+};
+
+}  // namespace blink
+
+#endif  // SKY_ENGINE_TONIC_DART_ISOLATE_SCOPE_H_