[Android WebView] Fix bugs with initial-scale between 0 and 1

The fix in https://chromiumcodereview.appspot.com/23754026 missed the
case of initial-scale, so fractional values were getting clamped to
zero incorrectly.  Secondly, initial-scale values should not be clamped
in WebView.

BUG=298962,282130,295886

Review URL: https://chromiumcodereview.appspot.com/24769002

git-svn-id: svn://svn.chromium.org/blink/trunk@158476 bbb929c8-8fbe-4397-9dbb-9b2b20218538