Revert 106677 (caused several PPAPI test timeouts, see http://crbug.com/101154)

ppapi/proxy/interface_proxy.cc

Index: ppapi/proxy/interface_proxy.cc
===================================================================
--- ppapi/proxy/interface_proxy.cc	(revision 106716)
+++ ppapi/proxy/interface_proxy.cc	(working copy)
@@ -21,5 +21,14 @@
   return dispatcher_->Send(msg);
 }
 
+uint32 InterfaceProxy::SendCallback(PP_CompletionCallback callback) {
+  return dispatcher_->callback_tracker().SendCallback(callback);
+}
+
+PP_CompletionCallback InterfaceProxy::ReceiveCallback(
+    uint32 serialized_callback) {
+  return dispatcher_->callback_tracker().ReceiveCallback(serialized_callback);
+}
+
 }  // namespace proxy
 }  // namespace ppapi