ActiveScriptWrappable: GC wrappers in detached ExecutionContexts.

third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.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 "bindings/core/v8/ActiveScriptWrappable.h"
 
+#include "bindings/core/v8/DOMDataStore.h"
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "bindings/core/v8/ScriptWrappableVisitor.h"
+#include "bindings/core/v8/V8Binding.h"
 #include "bindings/core/v8/V8PerIsolateData.h"
+#include "core/dom/ExecutionContext.h"
 
 namespace blink {
 
-ActiveScriptWrappable::ActiveScriptWrappable(ScriptWrappable* self)
+ActiveScriptWrappableBase::ActiveScriptWrappableBase(ScriptWrappable* self)
     : m_scriptWrappable(self) {
   ASSERT(ThreadState::current());
   v8::Isolate* isolate = ThreadState::current()->isolate();
   V8PerIsolateData* isolateData = V8PerIsolateData::from(isolate);
   isolateData->addActiveScriptWrappable(this);
 }
 
-void ActiveScriptWrappable::traceActiveScriptWrappables(
+void ActiveScriptWrappableBase::traceActiveScriptWrappables(
     v8::Isolate* isolate,
     ScriptWrappableVisitor* visitor) {
   V8PerIsolateData* isolateData = V8PerIsolateData::from(isolate);
   auto activeScriptWrappables = isolateData->activeScriptWrappables();
   if (!activeScriptWrappables) {
     return;
   }
 
   for (auto activeWrappable : *activeScriptWrappables) {
     auto scriptWrappable = activeWrappable->toScriptWrappable();
     if (!scriptWrappable->hasPendingActivity()) {
       continue;
     }
 
+    // Do not keep the wrapper alive if the ExecutionContext
+    // has become detached, irrespective of what hasPendingActivity()
+    // returns. This is done to avoid memory leaks. see

[Michael Lippautz, 2016/12/15 13:57:31]

nit: Mind copying over the comment? This part of MajorGCWrapperVisitor should go
away after wrapper tracing is enabled.

[sof, 2016/12/15 15:33:02]

Blended in that comment. Even though we invoke hasPendingActivity() always, it
is no longer considered a bug if it returns |true| when in a detached state. 

Writing up some general guidelines for hasPendingActivity() implementations,
would be worth doing.

+    // MajorGCWrapperVisitor::VisitPersistentHandle() comment.
+    if (activeWrappable->isContextDestroyed(activeWrappable)) {
+      continue;
+    }
     auto wrapperTypeInfo =
         const_cast<WrapperTypeInfo*>(scriptWrappable->wrapperTypeInfo());
     visitor->RegisterV8Reference(
         std::make_pair(wrapperTypeInfo, scriptWrappable));
   }
 }
 
 }  // namespace blink