Support exposing Mojo services between render frames, render threads, and their respective hosts.

content/public/test/mock_render_thread.cc

Index: content/public/test/mock_render_thread.cc
diff --git a/content/public/test/mock_render_thread.cc b/content/public/test/mock_render_thread.cc
index 0d1b0bcb6f3f9457f3db202b69475ebcbf1974e6..96bce949bbcc488081205588a57c2e990e82ffc8 100644
--- a/content/public/test/mock_render_thread.cc
+++ b/content/public/test/mock_render_thread.cc
@@ -188,6 +188,10 @@ void MockRenderThread::ReleaseCachedFonts() {
 
 #endif  // OS_WIN
 
+ServiceRegistry* MockRenderThread::GetServiceRegistry() {
+  return NULL;
+}
+
 void MockRenderThread::SendCloseMessage() {
   ViewMsg_Close msg(routing_id_);
   RenderViewImpl::FromRoutingID(routing_id_)->OnMessageReceived(msg);