PPAPI: Make blocking completion callbacks work.

ppapi/shared_impl/ppapi_globals.h

Index: ppapi/shared_impl/ppapi_globals.h
diff --git a/ppapi/shared_impl/ppapi_globals.h b/ppapi/shared_impl/ppapi_globals.h
index 8e2b94a8c8b35ba79e3a6acbeae7a96bbb867a0f..00fb9b16e12ef8e1f9151dca5172a71866fd4ab4 100644
--- a/ppapi/shared_impl/ppapi_globals.h
+++ b/ppapi/shared_impl/ppapi_globals.h
@@ -17,6 +17,7 @@
 
 namespace base {
 class Lock;
+class MessageLoopProxy;
 }
 
 namespace ppapi {
@@ -101,6 +102,11 @@ class PPAPI_SHARED_EXPORT PpapiGlobals {
   // failure.
   virtual PP_Module GetModuleForInstance(PP_Instance instance) = 0;
 
+  // Returns the base::MessageLoopProxy for the main thread. Note that this must
+  // be called on the main thread the first time so that it can initialize
+  // its static data.
+  base::MessageLoopProxy* GetMainThreadMessageLoop();
+
   // Returns the command line for the process.
   virtual std::string GetCmdLine() = 0;