Add GN isolate support for a bunch of unittests.
This enables the following tests to be run under
swarming on a GN bot:
- angle_unittests
- accessibility_unittests
- compositor_unittests
- cc_unittests
- ipc_tests
- gl_unittests
- sandbox_linux_unittests
- gn_unittests
- skia_unittests
- sql_unittests
- url_unittests
R=brettw@chromium.org, maruel@chromium.org
BUG=504079
CQ_EXTRA_TRYBOTS=tryserver.chromium.mac:mac_chromium_gn_rel
Review URL: https://codereview.chromium.org/
1248673005
Cr-Commit-Position: refs/heads/master@{#339973}