[lacros] Allow different behaviors when building and testing on bots

A temporary solution to allow different downloading behaviors when
building and testing on bots until version is pinned to chromium/src.

Bug: 1104318
Change-Id: I945a8be7f39a3762107791f70ff48cd09410b8d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315424Reviewed-by: Sven Zheng <svenzheng@chromium.org>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791537}

build/lacros/test_runner.py

@@ -113,13 +113,22 @@ def _remove_unused_ash_chrome_versions(version_to_skip):
           'past %d days', p, days)
       shutil.rmtree(p)
 
-def _DownloadAshChromeIfNecessary(version):
+
+def _DownloadAshChromeIfNecessary(version, is_download_for_bots=False):
   """Download a given version of ash-chrome if not already exists.
 
   Currently, a special constant version value is support: "for_bots", the reason
   is that version number is still not pinned to chromium/src, so a constant
   value is needed to make sure that after the builder who downloads and isolates
   ash-chrome, the tester knows where to look for the binary to use.
+  Additionally, a is_download_for_bots boolean argument is introduced to
+  indicate whether this function is downloading for bots specifically or
+  downloading while running tests, and it is needed because when version is
+  "for_bots", the expected behavior is different in the 2 scenarios: when
+  downloading for bots to isolate, we always want to update for_bots/ to reflect
+  the latest version; however, when downloading while running tests, we want to
+  skip updating to latest because swarming testers aren't supposed to have
+  external network access.
   TODO(crbug.com/1107010): remove the support once ash-chrome version is pinned
   to chromium/src.
 
@@ -140,7 +149,7 @@ def _DownloadAshChromeIfNecessary(version):
         os.path.join(ash_chrome_dir, 'chrome'))
 
   ash_chrome_dir = _GetAshChromeDirPath(version)
-  if version != 'for_bots' and IsAshChromeDirValid(ash_chrome_dir):
+  if not is_download_for_bots and IsAshChromeDirValid(ash_chrome_dir):
     return
 
   shutil.rmtree(ash_chrome_dir, ignore_errors=True)
@@ -150,7 +159,7 @@ def _DownloadAshChromeIfNecessary(version):
     gsutil = download_from_google_storage.Gsutil(
         download_from_google_storage.GSUTIL_DEFAULT_PATH)
     gs_version = (_GetLatestVersionOfAshChrome()
-                  if version == 'for_bots' else version)
+                  if is_download_for_bots else version)
     logging.info('Ash-chrome version: %s', gs_version)
     gs_path = _GS_URL_BASE + '/' + gs_version + '/' + _GS_ASH_CHROME_PATH
     exit_code = gsutil.call('cp', gs_path, tmp.name)
@@ -317,7 +326,7 @@ def Main():
       help='Download prebuilt ash-chrome for bots so that tests are hermetic '
       'during execution')
   download_parser.set_defaults(
-      func=lambda *_: _DownloadAshChromeIfNecessary('for_bots'))
+      func=lambda *_: _DownloadAshChromeIfNecessary('for_bots', True))
 
   test_parser = subparsers.add_parser('test', help='Run tests')
   test_parser.set_defaults(func=_RunTest)

build/lacros/test_runner_test.py

@@ -33,7 +33,7 @@ class TestRunnerTest(unittest.TestCase):
     args = ['script_name', 'download_for_bots']
     with mock.patch.object(sys, 'argv', args):
       test_runner.Main()
-      mock_download.assert_called_with('for_bots')
+      mock_download.assert_called_with('for_bots', True)
 
   @parameterized.expand([
       'url_unittests',