Show message every 30s for long running presubmits

Slow presubmits like CheckUnwantedDependencies can often take over 30s
to run. Print a "still running" message so users don't think something
hung.

Bug: b/358457858
Change-Id: I47f5589af43d8fb0f384e6f7c633e9d0addd568a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5782588
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Scott Lee <ddoman@chromium.org>

presubmit_support.py

@@ -1817,6 +1817,19 @@ class PresubmitExecuter(object):
             the result of the presubmit function call.
         """
         start_time = time_time()
+
+        def _progress_loop(event):
+            while not event.is_set():
+                if event.wait(timeout=30):
+                    return
+                sys.stdout.write(f'Still running {function_name} after '
+                                 f'{int(time_time() - start_time)}s...\n')
+
+        event = threading.Event()
+        event_thread = threading.Thread(target=_progress_loop, args=(event,))
+        event_thread.daemon = True
+        event_thread.start()
+
         try:
             result = eval(function_name + '(*__args)', context)
             self._check_result_type(result)
@@ -1827,6 +1840,9 @@ class PresubmitExecuter(object):
                     'Evaluation of %s failed: %s, %s' %
                     (function_name, e_value, traceback.format_exc()))
             ]
+        finally:
+            event.set()
+            event_thread.join()
 
         elapsed_time = time_time() - start_time
         if elapsed_time > 10.0: