Add a mojo channel for frame messages.

content/public/browser/render_frame_host.h

Index: content/public/browser/render_frame_host.h
diff --git a/content/public/browser/render_frame_host.h b/content/public/browser/render_frame_host.h
index 72cbc18bbafaea6d07ae5e29f5e9c42fc69c5d0a..c3bb0368831b06e329ac4a51981b345ea4a33d7c 100644
--- a/content/public/browser/render_frame_host.h
+++ b/content/public/browser/render_frame_host.h
@@ -10,6 +10,7 @@
 #include "base/callback_forward.h"
 #include "build/build_config.h"
 #include "content/common/content_export.h"
+#include "content/common/input/input_handler.mojom.h"
 #include "content/public/common/console_message_level.h"
 #include "content/public/common/file_chooser_params.h"
 #include "ipc/ipc_listener.h"
@@ -253,6 +254,8 @@ class CONTENT_EXPORT RenderFrameHost : public IPC::Listener,
 
   virtual bool IsFeatureEnabled(blink::WebFeaturePolicyFeature feature) = 0;
 
+  virtual mojom::FrameInputHandler* GetFrameInputHandler() = 0;
+
  private:
   // This interface should only be implemented inside content.
   friend class RenderFrameHostImpl;