[Android WebView] Add more tests for ClobberUserAgentInitialScaleQuirk

Added tests for cases when initial scale override _must_not_
be clobbered.

BUG=313754

Review URL: https://codereview.chromium.org/61793022

git-svn-id: svn://svn.chromium.org/blink/trunk@162105 bbb929c8-8fbe-4397-9dbb-9b2b20218538