[webnfc] Implement nfc.watch in blink nfc module.

third_party/WebKit/Source/modules/nfc/MessageCallback.h

Index: third_party/WebKit/Source/modules/nfc/MessageCallback.h
diff --git a/third_party/WebKit/Source/modules/nfc/MessageCallback.h b/third_party/WebKit/Source/modules/nfc/MessageCallback.h
index 046e277ef5c6e7b5016c835ee7dcf97872499fa0..43dcf0d531ca4ab33985b5978994a9d29b6aa6a6 100644
--- a/third_party/WebKit/Source/modules/nfc/MessageCallback.h
+++ b/third_party/WebKit/Source/modules/nfc/MessageCallback.h
@@ -10,12 +10,19 @@
 namespace blink {
 
 class NFCMessage;
+class ScriptState;
 
 class MessageCallback : public GarbageCollectedFinalized<MessageCallback> {
  public:
   virtual ~MessageCallback() {}
   DEFINE_INLINE_VIRTUAL_TRACE() {}
   virtual void handleMessage(const NFCMessage&) = 0;
+
+  void setScriptState(ScriptState* scriptState) { m_scriptState = scriptState; }
+  ScriptState* getScriptState() const { return m_scriptState.get(); }
+
+ private:
+  RefPtr<ScriptState> m_scriptState;
 };
 
 }  // namespace blink