Only copy the plugin if it doesn't already exist.
Only copy the plugin if it doesn't already exist.

CopyDirectory fails only on windows in this case.  Not sure how
it passed the try bots.

TBR=stuartmorgan

Review URL: http://codereview.chromium.org/2856088

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@54989 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