GTTF: Flip test launcher defaults (developer mode is now default)

chromium-dev discussions:
https://groups.google.com/a/chromium.org/d/msg/chromium-dev/ewfTWVUiYGw/uTlP2mOZlmAJ
https://groups.google.com/a/chromium.org/d/msg/chromium-dev/Mw1hrGwnUpw/pYVzC3o_SDQJ

BUG=236893
R=maruel@chromium.org, sky@chromium.org

Review URL: https://codereview.chromium.org/59623015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237448 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237448