Revert 159039 "Refactor fixed layout mode"

This broke WebViewTest.Shim_TestAutosizeWithPartialAttributes on Linux.

> Refactor fixed layout mode
> 
> Previously, the desktop browser would use FrameView's rect
> as the layout size while the mobile browser would enable
> "fixed layout mode" which then used a layoutSize variable
> that it could set instead.
> 
> This CL removes "fixed layout mode" as a FrameView concept
> and makes the layout size always an explicitly set property
> of the main FrameView. Another way to think about it is that
> we're now always in a fixed-layout, only we keep
> the layout size pegged to the window size (if the
> --enable-viewport flag is set, the layout size is set from
> @viewport/viewport meta).
> 
> Note: WebViewImpl still has a setFixedLayoutSize method 
> that's used by Android WebView.
> 
> BUG=285397
> 
> Review URL: https://codereview.chromium.org/23819019

TBR=bokan@chromium.org

Review URL: https://codereview.chromium.org/26401002

git-svn-id: svn://svn.chromium.org/blink/trunk@159063 bbb929c8-8fbe-4397-9dbb-9b2b20218538