Increase the prefetch experiment to 50/50 in dev & beta
Increase the prefetch experiment to 50/50 in dev & beta

I want more data on prefetch effectiveness, and so I'm upping it to
50/50 in dev & beta channels with this CL

BUG=NONE
TEST=NONE

Review URL: http://codereview.chromium.org/3396007

git-svn-id: http://src.chromium.org/svn/trunk/src@59552 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: b8a599224c67ef6aff3d1d3a64e3e335169da858
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