Add UMA tracing to requestIdleCallback.

Source/core/dom/ScriptedIdleTaskController.cpp

 // Copyright 2015 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 "config.h"
 #include "core/dom/ScriptedIdleTaskController.h"
 
 #include "core/dom/ExecutionContext.h"
 #include "core/dom/IdleRequestCallback.h"
 #include "platform/Logging.h"
@@ skipping 101 matching lines @@
     runCallback(id, deadlineSeconds, callbackType);
 }
 
 void ScriptedIdleTaskController::runCallback(CallbackId id, double deadlineSeconds, IdleDeadline::CallbackType callbackType)
 {
     ASSERT(!m_suspended);
     auto callback = m_callbacks.take(id);
     if (!callback)
         return;
 
+    double allotedTimeMillis = std::max((deadlineSeconds - monotonicallyIncreasingTime()) * 1000, 0.0);
+    Platform::current()->histogramCustomCounts("WebCore.ScriptedIdleTaskController.IdleCallbackDeadline", allotedTimeMillis, 0, 50, 50);
+
     // TODO(rmcilroy): Add devtools tracing.
     callback->handleEvent(IdleDeadline::create(deadlineSeconds, callbackType));
+
+    double overrunMillis = std::max((monotonicallyIncreasingTime() - deadlineSeconds) * 1000, 0.0);
+    Platform::current()->histogramCustomCounts("WebCore.ScriptedIdleTaskController.IdleCallbackOverrun", overrunMillis, 0, 10000, 50);
 }
 
 void ScriptedIdleTaskController::stop()
 {
     m_callbacks.clear();
 }
 
 void ScriptedIdleTaskController::suspend()
 {
     m_suspended = true;
@@ skipping 16 matching lines @@
         m_scheduler->postIdleTask(FROM_HERE, WTF::bind<double>(&internal::IdleRequestCallbackWrapper::idleTaskFired, callbackWrapper));
     }
 }
 
 bool ScriptedIdleTaskController::hasPendingActivity() const
 {
     return !m_callbacks.isEmpty();
 }
 
 } // namespace blink