Make a pre-read A/B field-trial

This CL disables/enables the Windows pre-read optimization based on a client-side coin-toss. The base::FieldTrial mechanism has not been used as it is not available until *after* chrome.dll is loaded, and this needs to occur before.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/7508034

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@95579 0039d316-1c4b-4281-b951-d872f2087c98
5 files changed