Use ChildFrameDisconnector when detaching child frames of a LocalFrame.

third_party/WebKit/Source/core/frame/RemoteFrame.cpp

Index: third_party/WebKit/Source/core/frame/RemoteFrame.cpp
diff --git a/third_party/WebKit/Source/core/frame/RemoteFrame.cpp b/third_party/WebKit/Source/core/frame/RemoteFrame.cpp
index f7eb7a08a368f0cd66401f2ba38e6a0867a15107..0c3c253a18989c5009bb8b7096b5c7f0d5847f40 100644
--- a/third_party/WebKit/Source/core/frame/RemoteFrame.cpp
+++ b/third_party/WebKit/Source/core/frame/RemoteFrame.cpp
@@ -196,4 +196,15 @@ void RemoteFrame::advanceFocus(WebFocusType type, LocalFrame* source)
     client()->advanceFocus(type, source);
 }
 
+void RemoteFrame::detachChildren()
+{
+    using FrameVector = HeapVector<Member<Frame>>;
+    FrameVector childrenToDetach;
+    childrenToDetach.reserveCapacity(tree().childCount());
+    for (Frame* child = tree().firstChild(); child; child = child->tree().nextSibling())
+        childrenToDetach.append(child);
+    for (const auto& child : childrenToDetach)
+        child->detach(FrameDetachType::Remove);
+}
+
 } // namespace blink