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..0803547b11071f28a0ff26f402ce12ffb468b718 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 +36,22 @@ void ActiveScriptWrappable::traceActiveScriptWrappables(
       continue;
     }
 
+    // A wrapper isn't kept alive after its ExecutionContext becomes
+    // detached, even if hasPendingActivity() returns |true|. This measure
+    // avoids memory leaks and has proven not to be too eager wrt
+    // garbage collection of objects belonging to discarded browser contexts
+    // ( https://html.spec.whatwg.org/#a-browsing-context-is-discarded )
+    //
+    // Consequently, an implementation of hasPendingActivity() is
+    // not required to take the detached state of the associated
+    // ExecutionContext into account (i.e., return |false|.) We probe
+    // the detached state of the ExecutionContext via
+    // |isContextDestroyed()|.
+    //
+    // TODO(haraken): Implement correct lifetime using traceWrapper.
+    if (activeWrappable->isContextDestroyed(activeWrappable)) {
+      continue;
+    }
     auto wrapperTypeInfo =
         const_cast<WrapperTypeInfo*>(scriptWrappable->wrapperTypeInfo());
     visitor->RegisterV8Reference(