Disallow UI/IO thread blocking on any other thread.

content/browser/renderer_host/render_widget_helper.cc

Index: content/browser/renderer_host/render_widget_helper.cc
===================================================================
--- content/browser/renderer_host/render_widget_helper.cc	(revision 133458)
+++ content/browser/renderer_host/render_widget_helper.cc	(working copy)
@@ -8,6 +8,7 @@
 #include "base/bind_helpers.h"
 #include "base/eintr_wrapper.h"
 #include "base/threading/thread.h"
+#include "base/threading/thread_restrictions.h"
 #include "content/browser/gpu/gpu_surface_tracker.h"
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "content/browser/renderer_host/render_view_host_impl.h"
@@ -148,6 +149,7 @@
     if (max_sleep_time <= base::TimeDelta::FromMilliseconds(0))
       break;
 
+    base::ThreadRestrictions::ScopedAllowWait allow_wait;
     event_.TimedWait(max_sleep_time);
   }