Fix non-useWideViewport initial-scale for Android WebView CTS test.

targetDensityDPIFactor was the value usually obtained from the previous
calculation in the case of small documents anyway.  The SetInitialScale
CTS test expects that the reported scale will always be
targetDensityDPIFactor * deviceScaleFactor even when the document is 
wider.

NOTRY=true
BUG=internal b/11061496

Review URL: https://codereview.chromium.org/27041003

git-svn-id: svn://svn.chromium.org/blink/trunk@159489 bbb929c8-8fbe-4397-9dbb-9b2b20218538