Renames CreateFakeNativeHandleFrame to FakeNativeHandle::CreateFrame and moves into test.gyp target 'fake_video_frames' which contains previous frame_generator target. Removes unused warnings from includers of webrtc/test/fake_texture_frame.h which did not use the function above. BUG=webrtc:5398 R=kjellander@webrtc.org TBR=stefan@webrtc.org Review URL: https://codereview.webrtc.org/1554223002 . Cr-Commit-Position: refs/heads/master@{#11149}