Reland "Streamline frame detach"

Source/web/WebFrame.cpp

Index: Source/web/WebFrame.cpp
diff --git a/Source/web/WebFrame.cpp b/Source/web/WebFrame.cpp
index c11f2e11122518e8ec0030f07e42c33a4bc5db89..d5498208d7dba748d3c4232433bc605c5315dd42 100644
--- a/Source/web/WebFrame.cpp
+++ b/Source/web/WebFrame.cpp
@@ -5,6 +5,7 @@
 #include "config.h"
 #include "public/web/WebFrame.h"
 
+#include "core/frame/FrameHost.h"
 #include "core/frame/RemoteFrame.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "platform/UserGestureIndicator.h"
@@ -122,6 +123,7 @@ void WebFrame::appendChild(WebFrame* child)
     }
 
     toCoreFrame(this)->tree().invalidateScopedChildCount();
+    toCoreFrame(this)->host()->incrementSubframeCount();
 }
 
 void WebFrame::removeChild(WebFrame* child)
@@ -141,6 +143,7 @@ void WebFrame::removeChild(WebFrame* child)
     child->m_previousSibling = child->m_nextSibling = 0;
 
     toCoreFrame(this)->tree().invalidateScopedChildCount();
+    toCoreFrame(this)->host()->decrementSubframeCount();
 }
 
 WebFrame* WebFrame::parent() const