Force DumpRenderTree to use the Mesa backend for OpenGL as was previously done for test_shell. Verified that Mesa will be used for WebGL tests after DRT dependencies are updated.
Force DumpRenderTree to use the Mesa backend for OpenGL as was
previously done for test_shell. Verified that Mesa will be used for
WebGL tests after DRT dependencies are updated.

BUG=none
TEST=none (ran a couple of WebGL tests in DRT via new-run-webkit-tests)

Review URL: http://codereview.chromium.org/3439007

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@59866 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