Call FrameView::contentsResized() when setting fixed layout size
https://bugs.webkit.org/show_bug.cgi?id=107922

Reviewed by James Robinson.

In fixed layout mode, we should be calling contentsResized() when the
fixed layout size is changed, but not laying out when the visible
content rect changes.

Previously landed as r140869 but was reverted due to a bug in bundled
Chromium-specific code. This patch includes just the minimum needed in
WebCore.

New WebFrameTest: FrameViewNeedsLayoutOnFixedLayoutResize.  Some
flaky and obsolete tests for the old page scale mode are also deleted.

Source/WebCore:

* page/FrameView.cpp:
(WebCore::FrameView::visibleContentsResized):
* platform/ScrollView.cpp:
(WebCore::ScrollView::setFixedLayoutSize):
(WebCore::ScrollView::setUseFixedLayout):

Source/WebKit/chromium:

* tests/WebFrameTest.cpp:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141450 268f45cc-cd09-0410-ab3c-d52691b4dbfc