Refactored the policy code to avoid BrowserThread.

The policy code now mostly uses TaskRunners, so that it can move into a
component without DEPS layering violations. The remaining classes that use
BrowserThread directly are meant to stay in //chrome and instantiate the policy
system.

Also cleaned up some unused includes and unused arguments.

This is a reland of https://codereview.chromium.org/26211008 after fixing
the configuration_policy=0 and clang builds.

BUG=271392
[email protected]

Review URL: https://codereview.chromium.org/29253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229605 0039d316-1c4b-4281-b951-d872f2087c98
52 files changed