v8binding: Makes WindowProxy::global_proxy_ a weak reference when detached.

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

Index: third_party/WebKit/Source/bindings/core/v8/LocalWindowProxy.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/LocalWindowProxy.cpp b/third_party/WebKit/Source/bindings/core/v8/LocalWindowProxy.cpp
index bf10fc7e30a1b85b215487a2c3430d0a0857a05c..8b7079feca3c7c48c87d48fa7e42d0b9bdf4f792 100644
--- a/third_party/WebKit/Source/bindings/core/v8/LocalWindowProxy.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/LocalWindowProxy.cpp
@@ -106,6 +106,12 @@ void LocalWindowProxy::DisposeContext(Lifecycle next_status) {
   V8GCForContextDispose::Instance().NotifyContextDisposed(
       GetFrame()->IsMainFrame());
 
+  if (next_status == Lifecycle::kFrameIsDetached) {
+    // The context's frame is detached from the DOM, so there shouldn't be a
+    // strong reference to the context.
+    global_proxy_.SetPhantom();
+  }
+
   DCHECK_EQ(lifecycle_, Lifecycle::kContextIsInitialized);
   lifecycle_ = next_status;
 }