Add a way to run only a fraction of the test.
Add a way to run only a fraction of the test.

--run-part=x:y runs the xth part out of yth.

X is 1 based.

example, to run all the tests in 3 runs :
--run-part=1:3
--run-part=2:3
--run-part=3:3

Review URL: http://codereview.chromium.org/42170

git-svn-id: http://src.chromium.org/svn/trunk/src@12448 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 8ae1b1b6fd53efbcce45c7c555c157df90720d11
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser