[blinkpy] Suppress stderr of git-cl by default

Bug: 953499
Change-Id: I0f7dfc4317b2de9bc92ef9900dd6888143133a84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1573879
Commit-Queue: Robert Ma <robertma@chromium.org>
Reviewed-by: Luke Z <lpz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652239}

third_party/blink/tools/blinkpy/common/net/git_cl.py

@@ -52,14 +52,22 @@ class GitCL(object):
         self._cwd = cwd
         self._git_executable_name = Git.find_executable_name(host.executive, host.platform)
 
-    def run(self, args, return_stderr=None):
-        """Runs git-cl with the given arguments and returns the output."""
+    def run(self, args, return_stderr=False):
+        """Runs git-cl with the given arguments and returns the output.
+
+        Args:
+            args: A list of arguments passed to `git cl`.
+            return_stderr: Whether to include stderr in the returned output (the
+                default is False because git-cl will show a warning when running
+                on Swarming bots with local git cache).
+
+        Returns:
+            A string (the output from git-cl).
+        """
         command = [self._git_executable_name, 'cl'] + args
         if self._auth_refresh_token_json and args[0] in _COMMANDS_THAT_TAKE_REFRESH_TOKEN:
             command += ['--auth-refresh-token-json', self._auth_refresh_token_json]
-        if return_stderr is not None:
-            return self._host.executive.run_command(command, cwd=self._cwd, return_stderr=return_stderr)
-        return self._host.executive.run_command(command, cwd=self._cwd)
+        return self._host.executive.run_command(command, cwd=self._cwd, return_stderr=return_stderr)
 
     def trigger_try_jobs(self, builders, bucket=None):
         """Triggers try jobs on the given builders.
@@ -103,8 +111,7 @@ class GitCL(object):
         return 'None'
 
     def _get_cl_status(self):
-        # Note: Don't return stderr to address crbug.com/946619
-        return self.run(['status', '--field=status'], return_stderr=False).strip()
+        return self.run(['status', '--field=status']).strip()
 
     def wait_for_try_jobs(
             self, poll_delay_seconds=10 * 60, timeout_seconds=120 * 60,