Add FeatureProvider::GetAPIFeatures, GetManifestFeatures, and
GetPermissionFeatures as shortcuts for FeatureProvider::GetByName.

R=yoz@chromium.org

Review URL: https://codereview.chromium.org/25943002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227338 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227338