Don't ignore size updates that have a width and height == 0.

It is perfectly legal for the Android WebView to have a zero height,
this is frequenly how a new WebView is first laid out. Rejecting the
initial (width, 0) size update causes the initial layout to be
too narrow.

BUG=344885

Review URL: https://codereview.chromium.org/172203003

git-svn-id: svn://svn.chromium.org/blink/trunk@167543 bbb929c8-8fbe-4397-9dbb-9b2b20218538