Don't resize the image to fit the window, if the image is being zoomed.

BUG=246455
R=jochen@chromium.org, tony@chromium.org

Review URL: https://codereview.chromium.org/18056006

git-svn-id: svn://svn.chromium.org/blink/trunk@156402 bbb929c8-8fbe-4397-9dbb-9b2b20218538