gpu: reference target surfaces through a globally unique surface id.

content/test/mock_render_thread.cc

Index: content/test/mock_render_thread.cc
diff --git a/content/test/mock_render_thread.cc b/content/test/mock_render_thread.cc
index 70de43e3d8e77c855acdeb37ae58f490f1cd919d..e52fd852ac170bc7d280cc4408d1d792b7dfb266 100644
--- a/content/test/mock_render_thread.cc
+++ b/content/test/mock_render_thread.cc
@@ -13,7 +13,7 @@
 namespace content {
 
 MockRenderThread::MockRenderThread()
-    : routing_id_(0), opener_id_(0) {
+    : routing_id_(0), surface_id_(0), opener_id_(0) {
 }
 
 MockRenderThread::~MockRenderThread() {
@@ -169,9 +169,11 @@ void MockRenderThread::SendCloseMessage() {
 // The Widget expects to be returned valid route_id.
 void MockRenderThread::OnMsgCreateWidget(int opener_id,
                                          WebKit::WebPopupType popup_type,
-                                         int* route_id) {
+                                         int* route_id,
+                                         int* surface_id) {
   opener_id_ = opener_id;
   *route_id = routing_id_;
+  *surface_id = surface_id_;
 }
 
 bool MockRenderThread::OnMessageReceived(const IPC::Message& msg) {