Add some tracing to most expensive accessibility functions.

content/browser/accessibility/browser_accessibility_manager.cc

Index: content/browser/accessibility/browser_accessibility_manager.cc
diff --git a/content/browser/accessibility/browser_accessibility_manager.cc b/content/browser/accessibility/browser_accessibility_manager.cc
index f84b62dea1121104265c1964752e304fddb1ff4e..bc5c08f97ad5f2b8ef24840c2eb4655d4e68b464 100644
--- a/content/browser/accessibility/browser_accessibility_manager.cc
+++ b/content/browser/accessibility/browser_accessibility_manager.cc
@@ -346,6 +346,9 @@ bool BrowserAccessibilityManager::UseRootScrollOffsetsWhenComputingBounds() {
 
 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();