Add some tracing to most expensive accessibility functions.

content/browser/accessibility/browser_accessibility_manager.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/browser/accessibility/browser_accessibility_manager.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 328 matching lines @@
 void BrowserAccessibilityManager::NavigationFailed() {
   user_is_navigating_away_ = false;
 }
 
 bool BrowserAccessibilityManager::UseRootScrollOffsetsWhenComputingBounds() {
   return true;
 }
 
 void BrowserAccessibilityManager::OnAccessibilityEvents(
     const std::vector<AXEventNotificationDetails>& details) {
+  TRACE_EVENT0("accessibility",
+               "BrowserAccessibilityManager::OnAccessibilityEvents");
+
   // Update the cached device scale factor.
   if (delegate_ && !use_custom_device_scale_factor_for_testing_)
     device_scale_factor_ = delegate_->AccessibilityGetDeviceScaleFactor();
 
   // Process all changes to the accessibility tree first.
   for (uint32_t index = 0; index < details.size(); ++index) {
     const AXEventNotificationDetails& detail = details[index];
     if (!tree_->Unserialize(detail.update)) {
       if (delegate_) {
         LOG(ERROR) << tree_->error();
@@ skipping 908 matching lines @@
       hit_test_result = parent;
     parent = parent->PlatformGetParent();
   }
 
   last_hover_ax_tree_id_ = hit_test_result->manager()->ax_tree_id();
   last_hover_node_id_ = hit_test_result->GetId();
   last_hover_bounds_ = hit_test_result->GetScreenBoundsRect();
 }
 
 }  // namespace content