Allow MainThreadEventQueue to call the RenderWidget directly.

Allocate the MainThreadEventQueue from the render widget allowing
a binding between then. This allows us to avoid
serialization/deserialization of events to IPC messages inside the
renderer. It also allows us to avoid jumping through a number of hoops
looking the input handler in a table. For example requesting a begin
main frame from the main thread doesn't require a hop to the compositor
and back to the main thread any more.

BUG=703344

Review-Url: https://codereview.chromium.org/2813683002
Cr-Commit-Position: refs/heads/master@{#466340}
diff --git a/content/renderer/idle_user_detector.h b/content/renderer/idle_user_detector.h
index 0fd24ed..1118cb6 100644
--- a/content/renderer/idle_user_detector.h
+++ b/content/renderer/idle_user_detector.h
@@ -28,6 +28,8 @@
   IdleUserDetector(RenderView* render_view);
   ~IdleUserDetector() override;
 
+  void ActivityDetected();
+
  private:
   // RenderViewObserver implementation:
   bool OnMessageReceived(const IPC::Message& message) override;