Force all tast tests to use local_test_runner.

This is a functional revert of https://chromium-review.googlesource.com/c/chromium/src/+/1553805

Turns out `cros_run_test --tast` doesn't exit non-zero if one of the tests
fail. So we've been ignoring failures since that landed. This reverts back
to using local_test_runner, which does reliably exit non-zero on failure.

Hard-coding the conditional instead of reverting the original CL to
avoid merge conflicts and for easier follow-up fixes.

Bug: 923426
Change-Id: Iaa49011061f42f062e79d0d6867f0741314d473b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1558494
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#648835}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 41e078e8a655634994f8169a5965990926bba98c

chromeos/test_runner.py

@@ -252,13 +252,16 @@ class TastTest(RemoteTest):
     # Coverage tests require some special pre-test setup, so use an
     # on_device_script in that case. For all other tests, use cros_run_test's
     # built-in '--tast' option. This gives us much better results reporting.
-    if self._llvm_profile_var:
+    # TODO(bpastene): s/True/self._llvm_profile_var/ once we parse Tast results.
+    if True:  # pylint: disable=using-constant-test
       # Build the shell script that will be used on the device to invoke the
       # test.
-      device_test_script_contents = self.BASIC_SHELL_SCRIPT[:] + [
-          'echo "LLVM_PROFILE_FILE=%s" >> /etc/chrome_dev.conf' % (
-              self._llvm_profile_var)
-      ]
+      device_test_script_contents = self.BASIC_SHELL_SCRIPT[:]
+      if self._llvm_profile_var:
+        device_test_script_contents += [
+            'echo "LLVM_PROFILE_FILE=%s" >> /etc/chrome_dev.conf' % (
+                self._llvm_profile_var)
+        ]
 
       local_test_runner_cmd = ['local_test_runner', '-waituntilready']
       if self._use_vm: