This is a trivial change, I just cutted and pasted part of the code in
screen_capturer_unittest.cc to screen_capturer_integration_test.cc, removed
DISABLED_ prefixes, and updated build file.
BUG=webrtc:6366
Review-Url: https://codereview.webrtc.org/2444583002
Cr-Commit-Position: refs/heads/master@{#14806}