Move host resource from the proxy to the shared_impl.

ppapi/proxy/ppb_buffer_proxy.cc

Index: ppapi/proxy/ppb_buffer_proxy.cc
diff --git a/ppapi/proxy/ppb_buffer_proxy.cc b/ppapi/proxy/ppb_buffer_proxy.cc
index 57dba6ca6f3ffbcad6ef9ee6f1f7a6c76ae1bffe..558b5316cd5cf6fb30e41c7b040791d53d4001b0 100644
--- a/ppapi/proxy/ppb_buffer_proxy.cc
+++ b/ppapi/proxy/ppb_buffer_proxy.cc
@@ -19,6 +19,8 @@
 #include "ppapi/thunk/ppb_buffer_trusted_api.h"
 #include "ppapi/thunk/thunk.h"
 
+using ppapi::HostResource;
+
 namespace pp {
 namespace proxy {
 
@@ -45,10 +47,6 @@ Buffer::~Buffer() {
   Unmap();
 }
 
-Buffer* Buffer::AsBuffer() {
-  return this;
-}
-
 ppapi::thunk::PPB_Buffer_API* Buffer::AsPPB_Buffer_API() {
   return this;
 }