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 5b33b551add3ebcd8d4971f046b663fa3eaf3eaf..a7241ae49e8435bd03ab0130bd88f76eeb8cee89 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"
@@ -263,6 +264,8 @@ 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;