Revert 242382 "Fix a race condition in preference metric reporting."

This broke android causing test crashes:
http://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20%28dbg%29/builds/17336/steps/chromiumtestshell_instrumentation_tests/logs/stdio
http://chromegw.corp.google.com/i/clank.tot/builders/instrumentation-yakju-clankium-tot/builds/21056/steps/Run%20stack%20tool%20with%20logcat%20dump/logs/stdio

> Fix a race condition in preference metric reporting.
> 
> Introduces:
> - PrefFilter: An interface to intercept preference values as they are loaded from disk, before any changes are possible.
> - PrefHashFilter: An implementation that verifies preference values against hashes in a PrefHashStore.
> - PrefHashStore(Impl): An interface and implementation for storing and verifying hashes of preferences.
> - PrefHashCalculator: A utility for calculating preference value hashes.
> 
> TBR=brettw (base/base.gyp), scottbyer (chrome/service/service_process_prefs.cc)
> BUG=321680
> NOTRY=True
> 
> Review URL: https://codereview.chromium.org/90563003

TBR=erikwright@chromium.org

Review URL: https://codereview.chromium.org/120803002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242388 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242388