AOSP/Gallery2 - Disable copying of arbitrary private file of Gallery2 into External Storage.

+ ContentResolver.SCHEME_FILE is a constant defined as "file". A malicious
  app can use "File:" url to copy private files of Gallery2.

  Fix is to lowercase the scheme before doing the comparison.

Fix: 201535427
Bug: 201535427
Test: manual
Change-Id: I40672a0745ac65549c539da73ebb5b1710fd2821
(cherry picked from commit 0acea168f86f938bc99d872a79558b46e4b61c39)