Add -logFile option to Bench

Logs to a file as well as stdout.  Useful for Android,
where logging takes a different format.
Review URL: https://codereview.appspot.com/6450095

git-svn-id: http://skia.googlecode.com/svn/trunk@4963 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed