Create a PPAPI host for new resource message routing.

ppapi/shared_impl/resource.h

Index: ppapi/shared_impl/resource.h
diff --git a/ppapi/shared_impl/resource.h b/ppapi/shared_impl/resource.h
index a68575433a04481eb1c4ba6b086154d6549f52e4..efe40daff329108adf70e824ed6b736dcfa1ea3c 100644
--- a/ppapi/shared_impl/resource.h
+++ b/ppapi/shared_impl/resource.h
@@ -65,6 +65,10 @@
   F(PPB_Widget_API) \
   F(PPB_X509Certificate_Private_API)
 
+namespace IPC {
+class Message;
+}
+
 namespace ppapi {
 
 // Forward declare all the resource APIs.
@@ -161,6 +165,22 @@ class PPAPI_SHARED_EXPORT Resource : public base::RefCounted<Resource> {
   // Template-based dynamic casting. See specializations below.
   template <typename T> T* GetAs() { return NULL; }
 
+  // Called when a PpapiPluginMsg_ResourceReply reply is received for a
+  // previous CallRenderer. The sequence number is the value returned the
+  // send function for the given request. The message is the nested reply
+  // message, which may be an empty message (depending on what the host
+  // sends).
+  //
+  // The default implementation will assert (if you send a request, you should
+  // override this function).
+  //
+  // (This function would make more conceptual sense on PluginResource but we
+  // need to call this function from general code that doesn't know how to
+  // distinguish the classes.)
+  virtual void OnReplyReceived(int sequence,
+                               int32_t result,
+                               const IPC::Message& msg);
+
  protected:
   // Logs a message to the console from this resource.
   void Log(PP_LogLevel_Dev level, const std::string& message);