Add remaining GN targets for the Linux gpu tests.

This patch adds support for the telemetry-based
gpu tests to the GN build, adds a stubbed out
target for angle_end2end_tests (full support
depends on angle GN fixes), and adds a dummy
'chromium_swarm_tests' build target.

With these fixes, it should be possible to flip the
linux_chromium_rel_ng bot to GN and still have
everything run.

R=kbr@chromium.org, brettw@chromium.org
BUG=519778

Review URL: https://codereview.chromium.org/1311913004

Cr-Commit-Position: refs/heads/master@{#346067}

• BUILD.gn[diff]
• chrome/BUILD.gn[diff]
• chrome/test/BUILD.gn[diff]
• gpu/BUILD.gn[diff]
• testing/buildbot/gn_isolate_map.pyl[diff]
• testing/buildbot/manage.py[diff]
• tools/mb/mb.py[diff]