Add trace event for detecting main frame in loading metrics.

content/renderer/render_frame_impl.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/render_frame_impl.h"
 
 #include <map>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 922 matching lines @@
       render_frame->blink_interface_provider_.get(),
       render_frame->blink_interface_registry_.get(), opener);
   render_frame->BindToWebFrame(web_frame);
   render_view->webview()->setMainFrame(web_frame);
   render_frame->render_widget_ = RenderWidget::CreateForFrame(
       widget_routing_id, hidden, screen_info, compositor_deps, web_frame);
   // TODO(avi): This DCHECK is to track cleanup for https://crbug.com/545684
   DCHECK_EQ(render_view->GetWidget(), render_frame->render_widget_)
       << "Main frame is no longer reusing the RenderView as its widget! "
       << "Does the RenderFrame need to register itself with the RenderWidget?";
+  TRACE_EVENT_INSTANT1("loading", "createMainFrame", TRACE_EVENT_SCOPE_THREAD,
+                       "frame", web_frame->frameIdForTracing());
+
   return render_frame;
 }
 
 // static
 void RenderFrameImpl::CreateFrame(
     int routing_id,
     int proxy_routing_id,
     int opener_routing_id,
     int parent_routing_id,
     int previous_sibling_routing_id,
@@ skipping 5916 matching lines @@
   // event target. Potentially a Pepper plugin will receive the event.
   // In order to tell whether a plugin gets the last mouse event and which it
   // is, we set |pepper_last_mouse_event_target_| to null here. If a plugin gets
   // the event, it will notify us via DidReceiveMouseEvent() and set itself as
   // |pepper_last_mouse_event_target_|.
   pepper_last_mouse_event_target_ = nullptr;
 #endif
 }
 
 }  // namespace content