Add prefixes to I/O data trace names so they can be distinguished on the waterfall.
Add prefixes to I/O data trace names so they can be distinguished on the
waterfall.

BUG=4173
TEST=look at page-cycler step on waterfall
Review URL: http://codereview.chromium.org/9658

git-svn-id: http://src.chromium.org/svn/trunk/src@4936 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 67f43c2669ca5cba014cfc3763bca9a61604cb7f
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