Revert 167342 "Fixed visible contents size calculation under sca..."

> Fixed visible contents size calculation under scale with scrollbars.
> 
> The visible contents rects calculated in FrameView didn't account
> properly for scrollbars when scaled. With the desktop pinch we need
> to include the fact that scrollbars will scale along with the page.
> This patch changes the visibleContentsRect method to subtract the
> scrollbar thickness only after converting to CSS pixels.
> 
> Additionally, WebViewImpl's method to clamp scroll offset at a
> certain scale also did not account for scaled scrollbars.
> 
> BUG=336539
> 
> Review URL: https://codereview.chromium.org/151453003

TBR=bokan@chromium.org

Review URL: https://codereview.chromium.org/170283016

git-svn-id: svn://svn.chromium.org/blink/trunk@167446 bbb929c8-8fbe-4397-9dbb-9b2b20218538