Move gn _run target generation into test(). (RELAND)

This is a reland of https://codereview.chromium.org/1653003006/

Consolidating the _run targets into the test template should make them
easier to maintain (and, eventually, remove).

BUG=583694
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1662053002

Cr-Original-Commit-Position: refs/heads/master@{#373385}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 3c0ef4309a77bbf172f081c99bbb33e732ea07af
1 file changed
tree: 9211f8776c377ffb318928cea3cd7cf56c10a3ae
  1. tools/