Reland "Streamline frame detach"

Source/core/page/Page.cpp

Index: Source/core/page/Page.cpp
diff --git a/Source/core/page/Page.cpp b/Source/core/page/Page.cpp
index 9dc655a814e403f5e0bb9d553a4929b778ff034c..58b55254fa045ae566a6440107170bad275641f8 100644
--- a/Source/core/page/Page.cpp
+++ b/Source/core/page/Page.cpp
@@ -128,7 +128,6 @@ Page::Page(PageClients& pageClients)
     , m_editorClient(pageClients.editorClient)
     , m_spellCheckerClient(pageClients.spellCheckerClient)
     , m_storageClient(pageClients.storageClient)
-    , m_subframeCount(0)
     , m_openedByDOM(false)
     , m_tabKeyCyclesThroughElements(true)
     , m_defersLoading(false)
@@ -441,19 +440,6 @@ double Page::timerAlignmentInterval() const
     return m_timerAlignmentInterval;
 }
 
-#if ENABLE(ASSERT)
-void Page::checkSubframeCountConsistency() const
-{
-    ASSERT(m_subframeCount >= 0);
-
-    int subframeCount = 0;
-    for (Frame* frame = mainFrame(); frame; frame = frame->tree().traverseNext())
-        ++subframeCount;
-
-    ASSERT(m_subframeCount + 1 == subframeCount);
-}
-#endif
-
 void Page::setVisibilityState(PageVisibilityState visibilityState, bool isInitialState)
 {
     if (m_visibilityState == visibilityState)