Send input event IPCs directly from the UI thread

content/browser/renderer_host/render_process_host_impl.h

Index: content/browser/renderer_host/render_process_host_impl.h
diff --git a/content/browser/renderer_host/render_process_host_impl.h b/content/browser/renderer_host/render_process_host_impl.h
index e46e2c511257b92098a5282633d58b3f1f738b0e..de40bf8385307a6c9f7b5d51a76078cea48d1653 100644
--- a/content/browser/renderer_host/render_process_host_impl.h
+++ b/content/browser/renderer_host/render_process_host_impl.h
@@ -135,6 +135,8 @@ class CONTENT_EXPORT RenderProcessHostImpl
   void SetSuddenTerminationAllowed(bool enabled) override;
   bool SuddenTerminationAllowed() const override;
   IPC::ChannelProxy* GetChannel() override;
+  IPC::Sender* GetImmediateSender() override;
+  IPC::Sender* GetIOThreadSender() override;
   void AddFilter(BrowserMessageFilter* filter) override;
   bool FastShutdownForPageCount(size_t count) override;
   bool FastShutdownStarted() const override;
@@ -291,8 +293,11 @@ class CONTENT_EXPORT RenderProcessHostImpl
   int32_t pending_views_;
 
  private:
-  friend class VisitRelayingRenderProcessHost;
+  class SafeSenderProxy;
+
   friend class ChildProcessLauncherBrowserTest_ChildSpawnFail_Test;
+  friend class SafeSenderProxy;
+  friend class VisitRelayingRenderProcessHost;
 
   std::unique_ptr<IPC::ChannelProxy> CreateChannelProxy(
       const std::string& channel_id);
@@ -300,6 +305,9 @@ class CONTENT_EXPORT RenderProcessHostImpl
   // Creates and adds the IO thread message filters.
   void CreateMessageFilters();
 
+  // Shared implementation for IPC::Senders exposed by this RPH.
+  bool SendImpl(IPC::Message* message, bool send_now);
+
   // Registers Mojo services to be exposed to the renderer.
   void RegisterMojoServices();
 
@@ -362,6 +370,10 @@ class CONTENT_EXPORT RenderProcessHostImpl
   base::FilePath GetEventLogFilePathWithExtensions(const base::FilePath& file);
 #endif
 
+  // An IPC::Sender which lives as long as this RPH and provides safe, opaque
+  // access to ChannelProxy SendNow() and SendOnIOThread().
+  const std::unique_ptr<SafeSenderProxy> safe_sender_;
+
   std::unique_ptr<MojoChildConnection> mojo_child_connection_;
   std::unique_ptr<MojoApplicationHost> mojo_application_host_;