Mojofy FrameHostMsg_FrameFocused.

Since this is the first RenderFrameHostProxy/RenderFrameProxy method to
be mojofied, this CL also adds the boilerplate for establishing a mojo
connection between RenderFrameHostProxy/RenderFrameProxy.

Change-Id: I9153eb01b7a5bef374823a067eaf793a48b6a3fe
Bug: 786836
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1643473
Commit-Queue: Lowell Manners <[email protected]>
Reviewed-by: Ken Rockot <[email protected]>
Reviewed-by: Alex Moshchuk <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/master@{#683111}
diff --git a/content/common/frame.mojom b/content/common/frame.mojom
index 769b35b..453b32e4 100644
--- a/content/common/frame.mojom
+++ b/content/common/frame.mojom
@@ -546,4 +546,7 @@
   ShowCreatedWindow(int32 pending_widget_routing_id,
                     ui.mojom.WindowOpenDisposition disposition,
                     gfx.mojom.Rect rect, bool opened_by_user_gesture);
+
+  // Sent by the renderer when the frame becomes focused.
+  FrameFocused();
 };