Add yet more GN isolates ...

Add yet more GN isolates ...

This should be almost everything left that is currently
running on the Linux GN bot.

- events_unittests
- extensions_browsertests
- extensions_unittests
- gcm_unit_tests
- gfx_unittests
- gpu_unittests
- jingle_unittests
- media_unittests
- mojo_common_unittests
- mojo_public_bindings_unittests
- mojo_public_environment_unittests
- nacl_loader_unittests
- net_unittests
- printing_unittests
- remoting_unittests
- sql_unittests (isolate existed, just swarmed)
- sync_integration_tests
- sync_unit_tests
- unit_tests

There are still more test steps that need isolates that are
not run on the GN bot, most notably browser_tests and interactive_ui_tests
(which is partially done in this CL but doesn't quite work right).

I'll get to those in upcoming CLs.

R=brettw@chromium.org
BUG=504079
CQ_EXTRA_TRYBOTS=tryserver.chromium.mac:mac_chromium_gn_rel

Review URL: https://codereview.chromium.org/1258753002

Cr-Commit-Position: refs/heads/master@{#341392}