Make <webview> use out-of-process iframe architecture.

extensions/common/guest_view/guest_view_messages.h

Index: extensions/common/guest_view/guest_view_messages.h
diff --git a/extensions/common/guest_view/guest_view_messages.h b/extensions/common/guest_view/guest_view_messages.h
index ac10c60c769ed99efab5001232d8b29ee2340d72..c9235f260c0ef50e0df05505bcb6ede945f4a444 100644
--- a/extensions/common/guest_view/guest_view_messages.h
+++ b/extensions/common/guest_view/guest_view_messages.h
@@ -53,3 +53,19 @@ IPC_MESSAGE_CONTROL4(GuestViewHostMsg_CreateMimeHandlerViewGuest,
                      std::string /* view_id */,
                      int /* element_instance_id */,
                      gfx::Size /* element_size */)
+
+// Tells a <webview> that its contentWindow is ready to be exposed.
+// The contentWindow should point to the RenderFrameProxy with routing
+// ID of |guest_proxy_routing_id|.
+IPC_MESSAGE_CONTROL2(GuestViewMsg_ContentWindowReady,
+                     int /* element_instance_id */,
+                     int /* guest_proxy_routing_id */)
+
+// We have a RenderFrame with routing id of |embedder_local_frame_routing_id|.
+// We want this local frame to be replaced with a remote frame that points
+// to a <webview>. This message will attach the local frame to the <webview>
+// guest. The <webview> is identified by its ID: |guest_instance_id|.
+IPC_MESSAGE_CONTROL3(GuestViewHostMsg_AttachLocalFrameToGuest,
+                     int /* embedder_local_frame_routing_id */,
+                     int /* element_instance_id */,
+                     int /* guest_instance_id */)