Convert chrome://policy to new WebUI style

This CL converts the chrome://policy page to the new WebUI style. The page
reuses as much CSS/JS from the überpage as possible to ensure consistency.

The CL also improves the page in many ways:
* Proper separation of policy value aggregation (C++) and
  presentation (WebUI)
* Better handling of policy values that overflow the available space
  (an extra table row can be toggled that shows the whole value)
* New PolicyUIHandler backend that will be shared with the imminent more
  user-friendly chrome://policy page (see bug 134849).
* Removal of dependency on JS templating engine with its copious use of
  eval().
* New browser test that verifies policy definitions and values are sent
  from the C++ backend to the WebUI and processed there correctly.

TEST=browser_tests and manual
BUG=chromium-os:26628

Review URL: https://chromiumcodereview.appspot.com/12084065

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@180684 0039d316-1c4b-4281-b951-d872f2087c98
10 files changed