Add some tracing to most expensive accessibility functions.

content/renderer/accessibility/blink_ax_tree_source.cc

 // Copyright 2014 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/accessibility/blink_ax_tree_source.h"
 
 #include <stddef.h>
 
 #include <set>
 
@@ skipping 367 matching lines @@
 blink::WebAXObject BlinkAXTreeSource::GetNull() const {
   return blink::WebAXObject();
 }
 
 void BlinkAXTreeSource::SerializeNode(blink::WebAXObject src,
                                       AXContentNodeData* dst) const {
   dst->role = AXRoleFromBlink(src.Role());
   dst->state = AXStateFromBlink(src);
   dst->id = src.AxID();
 
+  TRACE_EVENT1("accessibility", "BlinkAXTreeSource::SerializeNode", "role",
+               ui::ToString(dst->role));
+
   WebAXObject offset_container;
   WebFloatRect bounds_in_container;
   SkMatrix44 container_transform;
   src.GetRelativeBounds(offset_container, bounds_in_container,
                         container_transform);
   dst->location = bounds_in_container;
   if (!container_transform.isIdentity())
     dst->transform = base::WrapUnique(new gfx::Transform(container_transform));
   if (!offset_container.IsDetached())
     dst->offset_container_id = offset_container.AxID();
@@ skipping 484 matching lines @@
     return WebAXObject();
 
   WebDocument document = render_frame_->GetWebFrame()->GetDocument();
   if (!document.IsNull())
     return document.AccessibilityObject();
 
   return WebAXObject();
 }
 
 }  // namespace content