Reviewed by Gustavo Noronha Silva.

        [GTK] ScrollbarThemeGtk should be enabled for interior frame scrollbars
        https://bugs.webkit.org/show_bug.cgi?id=45046

        Make interior frame scrollbars "fully-fake," which means they do not rely
        at all on GTK+ for painting or behavior, but instead are typical WebCore
        scrollbars drawn according to the GTK+ theme. Move ScrollbarGtk to
        MainFrameScrollbarGtk and remove all logic in that file dealing with interior
        frame scrollbars.

        No new tests, as this is already covered by pixel tests for scrollbars,
        which were added in r66605.

        * GNUmakefile.am: Update sources list.
        * platform/ScrollView.h: Change the adjustment members to be smart pointers.
        * platform/Scrollbar.cpp: Enable THUMB_POSITION_AFFECTS_BUTTONS for GTK+ as well.
        * platform/gtk/MainFrameScrollbarGtk.cpp: Added.
        (MainFrameScrollbarGtk::create): Create a MainFrameScrollbarGtk instead of ScrollbarGtk.
        (MainFrameScrollbarGtk::MainFrameScrollbarGtk):
        (MainFrameScrollbarGtk::~MainFrameScrollbarGtk):
        (MainFrameScrollbarGtk::attachAdjustment):
        (MainFrameScrollbarGtk::detachAdjustment):
        (MainFrameScrollbarGtk::updateThumbPosition):
        (MainFrameScrollbarGtk::updateThumbProportion):
        (MainFrameScrollbarGtk::gtkValueChanged):
        (MainFrameScrollbarGtk::paint):
        * platform/gtk/MainFrameScrollbarGtk.h: Added.
        * platform/gtk/ScrollViewGtk.cpp:
        (WebCore::ScrollView::platformInit): Remove unnecessary initialization
        because of smart pointer change.
        (WebCore::ScrollView::createScrollbar): Instead of creating ScrollbarGtk for
        interior frame scrollbars, create a normal WebCore scrollbar.
        (WebCore::ScrollView::setGtkAdjustments): Added an extra assert which ensures
        that this method is never called with a non-null adjustment on an interior frame
        scrollbar.
        (WebCore::ScrollView::platformAddChild): Remove logic for interior frame scrollbars.
        (WebCore::ScrollView::platformRemoveChild): Remove logic for interior frame scrollbars.
        (WebCore::ScrollView::visibleContentRect): Use a more accurate guard for detecting
        transitionary states when accessing parent widgets. Explcitly guard against interior
        frame ScrollView's trying to determine size based on parent widgets.
        (WebCore::ScrollView::setScrollbarModes): This method was out of sync with the one
        it copy-and-pasted from. Update it and change the logic to do the right thing for
        interior frame scrollbars.
        * platform/gtk/ScrollbarGtk.cpp: Removed.
        * platform/gtk/ScrollbarGtk.h: Removed.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@66848 268f45cc-cd09-0410-ab3c-d52691b4dbfc