Also tweaked flakey test util to be less flakey, and resilient to
modifiers being held down.

BUG=302437

Review URL: https://codereview.chromium.org/115733010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242340 0039d316-1c4b-4281-b951-d872f2087c98
Add a --quic-version flag to specify a specific version of QUIC to use.

Review URL: https://codereview.chromium.org/116863004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242341 0039d316-1c4b-4281-b951-d872f2087c98
Gin: Spruce the README a bit.

Review URL: https://codereview.chromium.org/116953003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242342 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242341
SVN changes up to revision 242342