Revert 232342 "New prefetch histograms to get an idea of how oft..."

Broke the Linux Chromium OS ASAN Tests(3) bot.

> New prefetch histograms to get an idea of how often prefetches happen,
> what their success rate is, how often they're canceled, how long
> they take to load, and how big they are.
> 
> BUG=303816
> 
> Review URL: https://codereview.chromium.org/50493005

TBR=jkarlin@google.com

Review URL: https://codereview.chromium.org/55993002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232376 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232376