Back out previous round of bug 72747 changes due to Tp regression.

content/base/src/nsDocumentViewer.cpp

content/html/document/src/nsHTMLContentSink.cpp

content/html/document/src/nsHTMLDocument.h

content/html/document/src/nsIHTMLDocument.h

content/html/document/src/nsMediaDocument.cpp

content/xml/document/src/nsXMLContentSink.cpp

docshell/base/nsDocShell.cpp

docshell/base/nsDocShell.h

docshell/base/nsIScrollable.idl

embedding/browser/webBrowser/nsWebBrowser.cpp

layout/base/nsCSSFrameConstructor.cpp

layout/base/nsDocumentViewer.cpp

layout/base/public/nsIScrollableFrame.h

layout/generic/nsGfxScrollFrame.cpp

layout/generic/nsIScrollableFrame.h

layout/html/base/src/nsGfxScrollFrame.cpp

layout/html/style/src/nsCSSFrameConstructor.cpp