ActiveScriptWrappable: GC wrappers in detached ExecutionContexts.

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

Index: third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.cpp b/third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.cpp
index 2c44e04451016528612e51009012b2c17b843847..c7b2fff7c0edc75081afceb49502b2b2c1561802 100644
--- a/third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.cpp
@@ -4,13 +4,16 @@
 
 #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();
@@ -18,7 +21,7 @@ ActiveScriptWrappable::ActiveScriptWrappable(ScriptWrappable* self)
   isolateData->addActiveScriptWrappable(this);
 }
 
-void ActiveScriptWrappable::traceActiveScriptWrappables(
+void ActiveScriptWrappableBase::traceActiveScriptWrappables(
     v8::Isolate* isolate,
     ScriptWrappableVisitor* visitor) {
   V8PerIsolateData* isolateData = V8PerIsolateData::from(isolate);
@@ -33,6 +36,13 @@ void ActiveScriptWrappable::traceActiveScriptWrappables(
       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(