Fix scroll in page scaling mode.

Reviewed by Simon Fraser.

The following things are done in this patch:
1. Rename Frame::pageScaleFactor() to Frame::frameScaleFactor() to better
   reflect its purpose.
2. Frame::frameScaleFactor() returns the scale factor of this frame with
   respect to the container. So for the main frame it'll return the scale
   factor of the page, inner frames will return 1.0
3. scrollBy(), scrollX() and scrollY() to take into account of the frame
   scale factor, causing incorrect coordinates reported to Javascript.

Tests: fast/events/scale-and-scroll-body.html
       fast/events/scale-and-scroll-iframe-body.html
       fast/events/scale-and-scroll-iframe-window.html
       fast/events/scale-and-scroll-window.html

* html/HTMLBodyElement.cpp:
(WebCore::adjustForZoom):
(WebCore::HTMLBodyElement::setScrollLeft):
(WebCore::HTMLBodyElement::setScrollTop):
* loader/HistoryController.cpp:
(WebCore::HistoryController::saveScrollPositionAndViewStateToItem):
* page/DOMWindow.cpp:
(WebCore::DOMWindow::scrollX):
(WebCore::DOMWindow::scrollY):
(WebCore::DOMWindow::scrollTo):
* page/Frame.cpp:
(WebCore::Frame::frameScaleFactor): Return page's scale factor if this is
                                    main frame, otherwise 1.0
* page/Frame.h:
* page/FrameView.cpp:
(WebCore::FrameView::applyOverflowToViewport):
(WebCore::FrameView::scrollXForFixedPosition):
(WebCore::FrameView::scrollYForFixedPosition):

Source/WebKit2: https://bugs.webkit.org/show_bug.cgi?id=68081
Fix scroll in page scaling mode.

Reviewed by Simon Fraser.

* WebProcess/Plugins/PluginView.cpp: Rename pageScaleFactor to frameScaleFactor.
(WebKit::PluginView::handleEvent):
(WebKit::PluginView::viewGeometryDidChange):
(WebKit::PluginView::clipRectInWindowCoordinates):

LayoutTests: https://bugs.webkit.org/show_bug.cgi?id=68081
Add layout test for page scale and scrolling.

Reviewed by Simon Fraser.

Add tests to cover the following cases:
1. Scale and scroll window
2. Scale and scroll document.body
3. Scale and scroll iframe's contentWindow
4. Scale and scroll iframe's contentDocument.body

* fast/events/scale-and-scroll-body-expected.png: Added.
* fast/events/scale-and-scroll-body-expected.txt: Added.
* fast/events/scale-and-scroll-body.html: Added.
* fast/events/scale-and-scroll-iframe-body-expected.png: Added.
* fast/events/scale-and-scroll-iframe-body-expected.txt: Added.
* fast/events/scale-and-scroll-iframe-body.html: Added.
* fast/events/scale-and-scroll-iframe-window-expected.png: Added.
* fast/events/scale-and-scroll-iframe-window-expected.txt: Added.
* fast/events/scale-and-scroll-iframe-window.html: Added.
* fast/events/scale-and-scroll-window-expected.png: Added.
* fast/events/scale-and-scroll-window-expected.txt: Added.
* fast/events/scale-and-scroll-window.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@95715 268f45cc-cd09-0410-ab3c-d52691b4dbfc