Widen GPU trigger condition

GPU rasterization will be triggered when viewports meet either of the 
following conditions:
1) width=device-width, minimum-scale=X, where X >= 1.0
2) width=device-width, user-scalable=no

BUG=424469

Review URL: https://codereview.chromium.org/660133005

git-svn-id: svn://svn.chromium.org/blink/trunk@184566 bbb929c8-8fbe-4397-9dbb-9b2b20218538