Notify DevTools when updating frame in RenderWidget

content/renderer/render_widget.cc

 // Copyright (c) 2012 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_widget.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 809 matching lines @@
     needs_repainting_on_restore_ = true;
     TRACE_EVENT0("renderer", "EarlyOut_NotVisible");
     return;
   }
 
   if (is_accelerated_compositing_active_)
     using_asynchronous_swapbuffers_ = SupportsAsynchronousSwapBuffers();
 
   // Tracking of frame rate jitter
   base::TimeTicks frame_begin_ticks = base::TimeTicks::Now();
+  webwidget_->instrumentBeginFrame();
   AnimateIfNeeded();
 
   // Layout may generate more invalidation.  It may also enable the
   // GPU acceleration, so make sure to run layout before we send the
   // GpuRenderingActivated message.
   webwidget_->layout();
 
   // The following two can result in further layout and possibly
   // enable GPU acceleration so they need to be called before any painting
   // is done.
   UpdateTextInputState();
   UpdateSelectionBounds();
 
   // Suppress painting if nothing is dirty.  This has to be done after updating
   // animations running layout as these may generate further invalidations.
   if (!paint_aggregator_.HasPendingUpdate()) {
     TRACE_EVENT0("renderer", "EarlyOut_NoPendingUpdate");
     return;

[nduca, 2012/03/06 16:48:18]

If we early-return here, you'll generate a false frame marker *when* there is no
raf registered.

Ideally, you would check whether an animation is requested --- if not, then dont
mark the frame until after this branch. If an animation is requested, then mark
the frame begin where you are.

   }
 
   if (!last_do_deferred_update_time_.is_null()) {
     base::TimeDelta delay = frame_begin_ticks - last_do_deferred_update_time_;
     if (is_accelerated_compositing_active_) {
       UMA_HISTOGRAM_CUSTOM_TIMES("Renderer4.AccelDoDeferredUpdateDelay",
                                  delay,
                                  base::TimeDelta::FromMilliseconds(1),
                                  base::TimeDelta::FromMilliseconds(60),
                                  30);
@@ skipping 804 matching lines @@
   }
 }
 
 bool RenderWidget::WillHandleMouseEvent(const WebKit::WebMouseEvent& event) {
   return false;
 }
 
 bool RenderWidget::WebWidgetHandlesCompositorScheduling() const {
   return false;
 }