Use macros to define pepper interfaces

ppapi/proxy/ppp_video_decoder_proxy.h

Index: ppapi/proxy/ppp_video_decoder_proxy.h
diff --git a/ppapi/proxy/ppp_video_decoder_proxy.h b/ppapi/proxy/ppp_video_decoder_proxy.h
index 84346ba2b849a2392a880321b73b5b65e3d38065..e12c668bb120522601cacd8e089b1b1671600221 100644
--- a/ppapi/proxy/ppp_video_decoder_proxy.h
+++ b/ppapi/proxy/ppp_video_decoder_proxy.h
@@ -18,15 +18,11 @@ namespace proxy {
 
 class PPP_VideoDecoder_Proxy : public InterfaceProxy {
  public:
-  PPP_VideoDecoder_Proxy(Dispatcher* dispatcher, const void* target_interface);
+  PPP_VideoDecoder_Proxy(Dispatcher* dispatcher);
   virtual ~PPP_VideoDecoder_Proxy();
 
   static const Info* GetInfo();
 
-  const PPP_VideoDecoder_Dev* ppp_video_decoder_target() const {
-    return static_cast<const PPP_VideoDecoder_Dev*>(target_interface());
-  }
-
   // InterfaceProxy implementation.
   virtual bool OnMessageReceived(const IPC::Message& msg);
 
@@ -43,6 +39,11 @@ class PPP_VideoDecoder_Proxy : public InterfaceProxy {
   void OnMsgNotifyError(const ppapi::HostResource& decoder,
                         PP_VideoDecodeError_Dev error);
 
+  // When this proxy is in the plugin side, this value caches the interface
+  // pointer so we don't have to retrieve it from the dispatcher each time.
+  // In the host, this value is always NULL.
+  const PPP_VideoDecoder_Dev* ppp_video_decoder_impl_;
+
   DISALLOW_COPY_AND_ASSIGN(PPP_VideoDecoder_Proxy);
 };