media/PRESUBMIT.py: adding CheckPassByValue for base::Time and derived classes

media/PRESUBMIT.py

Index: media/PRESUBMIT.py
diff --git a/media/PRESUBMIT.py b/media/PRESUBMIT.py
index d87000bcc96d997f3ac684c54923c342e5446d21..02bd02bf01b13a3588e909b9ac1ea54eb4b71d68 100644
--- a/media/PRESUBMIT.py
+++ b/media/PRESUBMIT.py
@@ -8,6 +8,19 @@ See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into depot_tools.
 """
 
+import re
+import string
+
+# Well-defined simple classes containing only <= 4 ints, or <= 2 floats.
+BASE_TIME_TYPES = [
+    'base::Time',
+    'base::TimeDelta',
+    'base::TimeTicks',
+]
+
+BASE_TIME_TYPES_RE = re.compile(r'\bconst (%s)&' %
+                                string.join(BASE_TIME_TYPES, '|'))
+
 def _FilterFile(affected_file):
   """Return true if the file could contain code requiring a presubmit check."""
   return affected_file.LocalPath().endswith(
@@ -159,10 +172,29 @@ def _CheckForHistogramOffByOne(input_api, output_api):
   return []
 
 
+def _CheckPassByValue(input_api, output_api):
+  """Check that base::Time and derived classes are passed by value, and not by
+  const reference """
+
+  problems = []
+
+  for f in input_api.AffectedSourceFiles(_FilterFile):
+    for line_number, line in f.ChangedContents():
+      if BASE_TIME_TYPES_RE.search(line):
+        problems.append('%s:%d' % (f, line_number))
+
+  if problems:
+    return [output_api.PresubmitError(
+      'base::Time and derived classes should be passed by value and not by\n'
+      'const ref, see base/time/time.h for more information.', problems)]
+  return []
+
+
 def _CheckChange(input_api, output_api):
   results = []
   results.extend(_CheckForUseOfWrongClock(input_api, output_api))
   results.extend(_CheckForMessageLoopProxy(input_api, output_api))
+  results.extend(_CheckPassByValue(input_api, output_api))
   results.extend(_CheckForHistogramOffByOne(input_api, output_api))
   results += input_api.canned_checks.CheckPatchFormatted(input_api, output_api)
   return results