Add AppRTCMobileTestStubbedVideoIO to gn_isolate_map.
Add AppRTCMobileTestStubbedVideoIO to gn_isolate_map.

This will make it possible for the test to run on swarming bots.

BUG=chromium:685222
R=kjellander@webrtc.org
NOTRY=True

Review-Url: https://codereview.webrtc.org/2731423004
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#17113}

ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc