[Android WebView] In non-WideViewport mode, initial-scale < 1 must be ignored

From my experiments with the existing implementation, it turns out that in the
case when WideViewport is turned off, values of initial-scale < 1 are ignored in
most cases. The layout width is set to device-width (scaled according to
target-densitydpi). This also includes 'auto' initial-scale.

An exception from the rule is the case when width is set to device-width,
in which case the initial-scale is respected.

BUG=303189

Review URL: https://codereview.chromium.org/25353006

git-svn-id: svn://svn.chromium.org/blink/trunk@158922 bbb929c8-8fbe-4397-9dbb-9b2b20218538