Pass per-frame task runners to Workers (when possible) [2nd try]

third_party/WebKit/Source/core/workers/ParentFrameTaskRunners.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/workers/ParentFrameTaskRunners.h"
+
+#include "core/dom/ContextLifecycleObserver.h"
+#include "core/dom/Document.h"
+#include "public/platform/Platform.h"
+#include "wtf/Assertions.h"
+#include "wtf/ThreadingPrimitives.h"
+
+namespace blink {
+
+ParentFrameTaskRunners::ParentFrameTaskRunners(LocalFrame* frame)
+    : LocalFrameLifecycleObserver(frame)
+{
+    if (frame)
+        DCHECK(frame->document()->isContextThread());
+
+    // For now we only support very limited task types.
+    for (auto type : { TaskType::Internal, TaskType::Networking, TaskType::PostedMessage }) {
+        m_taskRunners.add(type, TaskRunnerHelper::get(type, frame));
+    }
+}
+
+WebTaskRunner* ParentFrameTaskRunners::get(TaskType type)
+{
+    MutexLocker lock(m_taskRunnersMutex);
+    return m_taskRunners.get(type);
+}
+
+DEFINE_TRACE(ParentFrameTaskRunners)
+{
+    LocalFrameLifecycleObserver::trace(visitor);
+}
+
+void ParentFrameTaskRunners::contextDestroyed()
+{
+    MutexLocker lock(m_taskRunnersMutex);
+    for (auto& entry : m_taskRunners)
+        entry.value = Platform::current()->currentThread()->getWebTaskRunner();
+}
+
+} // namespace blink