ActiveScriptWrappable: GC wrappers in detached ExecutionContexts.

third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.h

 // 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.
 
 #ifndef ActiveScriptWrappable_h
 #define ActiveScriptWrappable_h
 
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Noncopyable.h"
 
 namespace v8 {
 class Isolate;
 }
 
 namespace blink {
 
 class ScriptWrappable;
 class ScriptWrappableVisitor;
 
 /**
  * Classes deriving from ActiveScriptWrappable will be registered in a
  * thread-specific list. They keep their wrappers and dependant objects alive
  * as long as they have pending activity.
  */
-class CORE_EXPORT ActiveScriptWrappable : public GarbageCollectedMixin {
-  WTF_MAKE_NONCOPYABLE(ActiveScriptWrappable);
+class CORE_EXPORT ActiveScriptWrappableBase : public GarbageCollectedMixin {
+  WTF_MAKE_NONCOPYABLE(ActiveScriptWrappableBase);
 
  public:
-  explicit ActiveScriptWrappable(ScriptWrappable*);
+  explicit ActiveScriptWrappableBase(ScriptWrappable*);
 
   static void traceActiveScriptWrappables(v8::Isolate*,
                                           ScriptWrappableVisitor*);
 
+ protected:
+  virtual bool isContextDestroyed(ActiveScriptWrappableBase*) const = 0;
+
  private:
   ScriptWrappable* toScriptWrappable() const { return m_scriptWrappable; }
 
   ScriptWrappable* m_scriptWrappable;
 };
 
+template <typename T>
+class CORE_EXPORT ActiveScriptWrappable : public ActiveScriptWrappableBase {
+  WTF_MAKE_NONCOPYABLE(ActiveScriptWrappable);
+
+ public:
+  explicit ActiveScriptWrappable(ScriptWrappable* wrappable)
+      : ActiveScriptWrappableBase(wrappable) {}
+
+ protected:
+  bool isContextDestroyed(ActiveScriptWrappableBase* object) const final {
+    return !(static_cast<T*>(object)->T::getExecutionContext)() ||

[haraken, 2016/12/15 15:35:06]

You're clever!

I'm surprised that all ActiveScriptWrappable objects already have
getExecutionContext)(). Is it because all ActiveScriptWrappable objects inherit
from EventTarget by accident?

[sof, 2016/12/15 15:47:39]

Or ContextLifecycleObserver.. or both (in which case it already needs to
disambiguate, so this will behave as wanted.)

+           (static_cast<T*>(object)->T::getExecutionContext)()
+               ->isContextDestroyed();
+  }
+};
+
 }  // namespace blink
 
 #endif  // ActiveScriptWrappable_h