FrameView resizes should always cause fixed-pos elements to relayout.

FrameView::viewportConstrainedVisibleContentSizeChanged had an early out when
viewportEnabled was off since it assumed changing the FrameView's size otherwise
would cause a relayout. With changes in the virtual-viewport model that's no
longer strictly the case. When a resize comes into Blink, we change the
FrameView's layout size. After layout completes we resize the FrameView's
rect. We do this so we can size the FrameView to be the size of the viewport at
minimum scale (i.e. content size on Android). On desktop, the layout size and
the FrameView rect will typically be one and the same, so when we resized the
rect in refreshPageScaleFactorAfterLayout() the layout size didn't change so we
didn't do a layout.

This was causing a bug in ChromeOS OOBE where the keyboard resizing the WebUI
would cause the fixed-pos shelf to appear in the wrong place and cut off pieces
of the UI.

This patch removes the early out if we're in virtual viewport pinch zoom mode.
In this mode, I also removed the call to
viewportConstrainedVisibleContentSizeChanged from setPageScaleFactor since the
new mode doesn't relayout fixed-pos elements when pinch-zooming.

BUG=361157

Review URL: https://codereview.chromium.org/287073002

git-svn-id: svn://svn.chromium.org/blink/trunk@174417 bbb929c8-8fbe-4397-9dbb-9b2b20218538