Add permission checks for PPB_Buffer.
BUG=116317
TEST=browser_tests

Review URL: https://chromiumcodereview.appspot.com/11446075

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@171951 0039d316-1c4b-4281-b951-d872f2087c98
thunk::PPB_Buffer_API* Buffer::AsPPB_Buffer_API() {
  return this;
}

thunk::PPB_Buffer_API* Buffer::AsPPB_Buffer_API() {
  return this;
}
