Add isolate files for Android tests

BUG=chromium:583318
TESTED=Passing runs with:
GYP_DEFINES='test_isolation_mode=prepare OS=android' webrtc/build/gyp_webrtc
ninja -C out/Release
NOTRY=True
NOPRESUBMIT=True

Review URL: https://codereview.webrtc.org/1882963003

Cr-Original-Commit-Position: refs/heads/master@{#12397}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: e532aec25220f94830c538acfeccc2203b6db4f5
28 files changed