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 {
 
+ContextObserver::ContextObserver(LocalFrame* frame)
+    : m_executionContext(frame ? frame->document() : nullptr) {}

[sof, 2016/12/19 09:14:03]

Can BarProp be changed to be over Document* instead? then we don't need this
constructor.

[haraken, 2016/12/19 09:58:15]

I can, but as far as I grep the code base, there are many classes that need to
retrieve a document from a frame. So it looks better to have a helper.

+
+ExecutionContext* ContextObserver::getExecutionContext() const {
+  return m_executionContext && !m_executionContext->isContextDestroyed()
+             ? m_executionContext
+             : nullptr;
+}
+
+LocalFrame* ContextObserver::frame() const {
+  return m_executionContext && m_executionContext->isDocument()
+             ? toDocument(m_executionContext)->frame()
+             : nullptr;
+}
+
+DEFINE_TRACE(ContextObserver) {
+  visitor->trace(m_executionContext);
+}
+
 LocalFrame* ContextLifecycleObserver::frame() const {
   return getExecutionContext() && getExecutionContext()->isDocument()
              ? toDocument(getExecutionContext())->frame()
              : nullptr;
 }
 }