Fixed unused variable(s) in the generated policy schema data.

Some static data is generated at runtime based on the list of supported policies
for that build, which is used at runtime to validate the policies loaded by
Chrome. Depending on the types of policies supported, some platforms may not
use all of the generated data.

This CL avoids generating data that isn't used, and prevents build failures
due to unused variables when that happens.

BUG=None

Review URL: https://codereview.chromium.org/145013009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246613 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246613
Switch ExternalPolicyDataUpdater from SHA-1 to SHA-256

This CL switches the hash algorithm used by ExternalPolicyDataUpdater
from SHA-1 to SHA-256. Since neither of the two features using this code
(policy for extensions and the UserAvatar Image policy) has been released
yet, there is no need for backwards compatibility.

BUG=336874
TEST=Updated tests

Review URL: https://codereview.chromium.org/135973006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246615 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246615