Move DumpRenderTree.gyp into Source/testing and get rid of the directory.

Now that Chromium moved away of it we can remove it from Blink.

R=abarth@chromium.org

Review URL: https://chromiumcodereview.appspot.com/22763006

git-svn-id: svn://svn.chromium.org/blink/trunk@155900 bbb929c8-8fbe-4397-9dbb-9b2b20218538