PPAPI: Make blocking completion callbacks work.

ppapi/shared_impl/ppapi_globals.cc

Index: ppapi/shared_impl/ppapi_globals.cc
diff --git a/ppapi/shared_impl/ppapi_globals.cc b/ppapi/shared_impl/ppapi_globals.cc
index c453ae2d4854b86bd3dcd568abbb66d079abd95f..80a4ee2417fc8ecb448fde261f411f8284abe73c 100644
--- a/ppapi/shared_impl/ppapi_globals.cc
+++ b/ppapi/shared_impl/ppapi_globals.cc
@@ -6,6 +6,7 @@
 
 #include "base/lazy_instance.h"  // For testing purposes only.
 #include "base/logging.h"
+#include "base/message_loop_proxy.h"
 #include "base/threading/thread_local.h"  // For testing purposes only.
 
 namespace ppapi {
@@ -41,6 +42,12 @@ void PpapiGlobals::SetPpapiGlobalsOnThreadForTest(PpapiGlobals* ptr) {
   tls_ppapi_globals_for_test.Pointer()->Set(ptr);
 }
 
+base::MessageLoopProxy* PpapiGlobals::GetMainThreadMessageLoop() {
+  CR_DEFINE_STATIC_LOCAL(scoped_refptr<base::MessageLoopProxy>, proxy,
+      (base::MessageLoopProxy::current()));
+  return proxy.get();
+}
+
 bool PpapiGlobals::IsHostGlobals() const {
   return false;
 }