GTTF: enable new test launcher for gpu_unittests

Note that this is behind a flag for now, --brave-new-test-launcher.

Makes gpu_unittests take 3s instead of 10s on my workstation.

BUG=299202
R=piman@chromium.org

Review URL: https://codereview.chromium.org/25050006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226081 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226081
<webview>: Update WebviewOverrideUserAgentFunction to inherit from common class

WebviewExtensionFunction was recently added to move the WebViewGuest security
check to a common base class.

BUG=none

Review URL: https://codereview.chromium.org/25073003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226082 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226082