Detach old frame on WebFrame::swap.

Source/core/frame/Frame.h

Index: Source/core/frame/Frame.h
diff --git a/Source/core/frame/Frame.h b/Source/core/frame/Frame.h
index 2bdfd460cef7a7b0a9ae3e8bc800dc332a701d27..77ed43bfdf68fab5c7a64f7c273a3c2822b84595 100644
--- a/Source/core/frame/Frame.h
+++ b/Source/core/frame/Frame.h
@@ -55,6 +55,8 @@ class WindowProxy;
 class WindowProxyManager;
 struct FrameLoadRequest;
 
+enum class FrameDetachType { Remove, Swap };
+
 // Status of user gesture.
 enum class UserGestureStatus { Active, None };
 
@@ -76,7 +78,7 @@ public:
     virtual void navigate(const FrameLoadRequest&) = 0;
     virtual void reload(FrameLoadType, ClientRedirectPolicy) = 0;
 
-    virtual void detach();
+    virtual void detach(FrameDetachType);
     void detachChildren();
     virtual void disconnectOwnerElement();
 
@@ -103,6 +105,12 @@ public:
     Frame* findFrameForNavigation(const AtomicString& name, Frame& activeFrame);
     Frame* findUnsafeParentScrollPropagationBoundary();
 
+    // This prepares the Frame for the next commit. It will detach children,
+    // dispatch unload events, abort XHR requests and detach the document.
+    // Returns true if the frame is ready to receive the next commit, or false
+    // otherwise.
+    virtual bool prepareForCommit() = 0;
+    void prepareSwapFrom(Frame*);
     void finishSwapFrom(Frame*);
 
     bool canNavigate(const Frame&);