bindings: Use V8 MaybeLocal<> APIs in Dictionary class

Source/bindings/core/v8/Dictionary.h

Index: Source/bindings/core/v8/Dictionary.h
diff --git a/Source/bindings/core/v8/Dictionary.h b/Source/bindings/core/v8/Dictionary.h
index 5860f34414e00be8276216d35edc9ca8d684d6e0..172f8199eb8656e268472375e6359e68430a15ce 100644
--- a/Source/bindings/core/v8/Dictionary.h
+++ b/Source/bindings/core/v8/Dictionary.h
@@ -29,6 +29,7 @@
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/Nullable.h"
+#include "bindings/core/v8/ScriptState.h"
 #include "bindings/core/v8/ScriptValue.h"
 #include "bindings/core/v8/V8Binding.h"
 #include "bindings/core/v8/V8BindingMacros.h"
@@ -44,12 +45,12 @@ namespace blink {
 // Dictionary class provides ways to retrieve property values as C++ objects
 // from a V8 object. Instances of this class must not outlive V8's handle scope
 // because they hold a V8 value without putting it on persistent handles.
-class Dictionary {
+class Dictionary : public ScriptState::Observer {
     ALLOW_ONLY_INLINE_ALLOCATION();
 public:
     Dictionary();
     Dictionary(const v8::Handle<v8::Value>& options, v8::Isolate*, ExceptionState&);
-    ~Dictionary();
+    virtual ~Dictionary();
 
     Dictionary& operator=(const Dictionary&);
 
@@ -120,11 +121,21 @@ public:
     bool hasProperty(const String&) const;
 
     v8::Isolate* isolate() const { return m_isolate; }
+    // Used by DictionaryHelper. This context could be an empty handle and
+    // should be used only for V8 APIs which return MaybeLocal<T>.
+    v8::Local<v8::Context> context() const { return m_context; }
 
     bool getKey(const String& key, v8::Local<v8::Value>&) const;
 
 private:
+    // ScriptState::Observer implementation
+    virtual void willDisposeScriptState(ScriptState*) override;
+
+    void subscribeScriptStateDisposal();
+    void unsubscribeScriptStateDisposal();
+
     v8::Handle<v8::Value> m_options;
+    v8::Local<v8::Context> m_context;
     v8::Isolate* m_isolate;
     ExceptionState* m_exceptionState;
 };