Mac: don't scale theme overlay image.
Mac: don't scale theme overlay image.

BUG=27214
TEST=Install Porsche theme. Change the window size. The silhouette of the Porsche should stay the same size (and not be stretche), remain the same absolute distance from the left, and be clipped off (and not shown) when the window is too narrow. Compare the behaviour on Windows.

Review URL: http://codereview.chromium.org/545018

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@35965 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser