[Android WebView] Scale the layout width by the UA initial scale

Another subtle difference of the Classic WebView implementation. In non-wide
viewport mode, the UA initial scale (set via 'setInitialPageScaleOverride')
can stretch the resulting layout width.

BUG=315552

Review URL: https://codereview.chromium.org/59073007

git-svn-id: svn://svn.chromium.org/blink/trunk@161551 bbb929c8-8fbe-4397-9dbb-9b2b20218538