Add chrome-search: access from Instant overlay

Enables the Instant NTP page access to:
  chrome-search://theme/*,
  chrome-search://favicon/*, and
  chrome-search://thumb/*.

This CL has a number of aspects to make the installed theme
background image available to the Instant overlay:
   1. Utilizes the new chrome-search: scheme that is accessible only
      to the Instant overlay's render process.  This is enforced
      on the renderer side by WebKit::WebSecurityPolicy
      facilities.  This is enforced on the browser side by the
      InstantIOContext::ShouldServiceRequest and URLDataSource::ShouldServiceRequest facilities.
   2. Whitelists the chrome-search://theme origin to be made
      available to the specific Instant overlay's origin/url.
   3. Backend CSS that sets the appropriate background image
      that resides in the chrome-search://theme origin.
   4. A small refactoring of the Instant tests to support mix-in
      usage of InstantTestBase.

BUG=172408, 134937
TEST=InstantPolicyTest.SearchSchemePolicy
R=sreeram@chromium.org, creis@chromium.org


Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=186347

Review URL: https://chromiumcodereview.appspot.com/11896113

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@186680 0039d316-1c4b-4281-b951-d872f2087c98

0 files changed, 0 insertions, 0 deletions