Introduce ContextObserver

third_party/WebKit/Source/core/dom/ContextLifecycleObserver.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/ContextLifecycleObserver.h"
 
 #include "core/dom/Document.h"
 #include "core/frame/LocalFrame.h"
 
 namespace blink {
 
+ContextClient::ContextClient(LocalFrame* frame)
+    : m_executionContext(frame ? frame->document() : nullptr) {}
+
+ExecutionContext* ContextClient::getExecutionContext() const {
+  return m_executionContext && !m_executionContext->isContextDestroyed()
+             ? m_executionContext
+             : nullptr;
+}
+
+LocalFrame* ContextClient::frame() const {
+  return m_executionContext && m_executionContext->isDocument()
+             ? toDocument(m_executionContext)->frame()
+             : nullptr;
+}
+
+DEFINE_TRACE(ContextClient) {
+  visitor->trace(m_executionContext);
+}
+
 LocalFrame* ContextLifecycleObserver::frame() const {
   return getExecutionContext() && getExecutionContext()->isDocument()
              ? toDocument(getExecutionContext())->frame()
              : nullptr;
 }
 }