Reviewed by Anders Carlsson.

        Improve scale factor resetting
        https://bugs.webkit.org/show_bug.cgi?id=53093
        
        Two key changes:
        - Don't set the scale factor to what it already is, as this causes an
        uneeded force layout and scroll
        - Don't ever set the scale factor based on a non-main frame committing
        
        This fixes two WebKit2 layout tests.

        * WebProcess/WebCoreSupport/WebFrameLoaderClient.cpp:
        (WebKit::WebFrameLoaderClient::dispatchDidCommitLoad):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@76604 268f45cc-cd09-0410-ab3c-d52691b4dbfc