cc: Fix comment in ContextProvider header.

R=jamesr
BUG=
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/23449046

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224737 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224737