Include original traceback in _run_check_function.

This is a followup to CL:2797935 to make it easier to debug exceptions.

Bug: 1206782
Change-Id: Ibb649e94fd562919737de152e3203ca6b02b38ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2880843Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Allen Webb <allenwebb@google.com>

presubmit_support.py

@@ -1661,7 +1661,16 @@ class PresubmitExecuter(object):
       if sink:
         elapsed_time = time_time() - start_time
         sink.report(function_name, rdb_wrapper.STATUS_FAIL, elapsed_time)
-      raise type(e)('Evaluation of %s failed: %s' % (function_name, e))
+      # TODO(crbug.com/953884): replace raise_from with native py3:
+      #   raise .. from e
+      try:
+        from future.utils import raise_from
+        raise_from(type(e)('Evaluation of %s failed: %s' % (function_name, e)),
+                   e)
+      except ImportError:
+        if self.verbose:
+          traceback.print_exc()
+        raise type(e)('Evaluation of %s failed: %s' % (function_name, e))
 
     if sink:
       elapsed_time = time_time() - start_time