Allow running browser tests each in single-process mode. This is useful for Android team, which wan…

Allow running browser tests each in single-process mode. This is useful for Android team, which want to run every test in content_browsertests in single-process mode. Browser tests need to run in separate processes though, each since browser initialization can't happen twice.

Currently, if --single-process is specified, the second test run will assert because of the multiple browser-process initialization problem. This change makes it so that it works as expected. However, it will still fail as before if --single-process and --gtest_filter=<multiple_tests> is passed.
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=156107

[sky, 2012-09-11 17:39:47]

LGTM