Add TaskRunnerHelper::get for Frame that casts to LocalFrame if possible or uses nullptr.

third_party/WebKit/Source/core/dom/TaskRunnerHelper.cpp

 // Copyright 2016 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 "core/dom/TaskRunnerHelper.h"
 
 #include "core/dom/Document.h"
 #include "core/frame/LocalFrame.h"
 #include "platform/WebFrameScheduler.h"
 #include "platform/WebTaskRunner.h"
@@ skipping 30 matching lines @@
       return frame ? frame->frameScheduler()->loadingTaskRunner()
                    : Platform::current()->currentThread()->getWebTaskRunner();
     case TaskType::Unthrottled:
       return frame ? frame->frameScheduler()->unthrottledTaskRunner()
                    : Platform::current()->currentThread()->getWebTaskRunner();
   }
   NOTREACHED();
   return nullptr;
 }
 
+RefPtr<WebTaskRunner> TaskRunnerHelper::get(TaskType type, Frame* frame) {
+  return get(type, frame->isLocalFrame() ? toLocalFrame(frame) : nullptr);
+}
+
 RefPtr<WebTaskRunner> TaskRunnerHelper::get(TaskType type, Document* document) {
   return get(type, document ? document->frame() : nullptr);
 }
 
 RefPtr<WebTaskRunner> TaskRunnerHelper::get(
     TaskType type,
     ExecutionContext* executionContext) {
   return get(type, executionContext && executionContext->isDocument()
                        ? static_cast<Document*>(executionContext)
                        : nullptr);
 }
 
 RefPtr<WebTaskRunner> TaskRunnerHelper::get(TaskType type,
                                             ScriptState* scriptState) {
   return get(type, scriptState ? scriptState->getExecutionContext() : nullptr);
 }
 
 }  // namespace blink