AVFoundation NSString*, cache them in the AVFoundationInternal LazyInstance.

Currently there's a symbol retrieval in place every time someone asks for
a NSString* inside the AVFoundation library. Change this so that the
AVFoundationInternal retrieves them on construction and caches them. This
CL should not change the behaviour of the avfoundation_glue.

BUG=323536, 288562

Review URL: https://codereview.chromium.org/137903003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245132 0039d316-1c4b-4281-b951-d872f2087c98
Removed the old policy protobufs location.

The policy protobufs were duplicated at chrome/browser/policy/proto
so that the protofiles ebuild of ChromeOS could still fetch them.
That ebuild has been fixed in a separate CL at:

  https://chromium-review.googlesource.com/#/c/182300/

BUG=327345

Review URL: https://codereview.chromium.org/137903004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245133 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245133