[Android WebView] Fix UA initial scale clobber code

A follow-up for https://codereview.chromium.org/55073002/

Apparently, the committed conditions for clobbering the UA-specified
initial scale were not matching the CL description :)

I have also noticed that, depending on ViewportMetaLayoutSizeQuirk state,
width's ExtendToZoom type may or may not be converted into Auto,
so I extended existing checks for 'isAuto' with checks for 'ExtendToZoom'.

BUG=304548, 313754

Review URL: https://codereview.chromium.org/69933011

git-svn-id: svn://svn.chromium.org/blink/trunk@161970 bbb929c8-8fbe-4397-9dbb-9b2b20218538