cc: Add presubmit that IPC should be updated with mojo

IPC serialization is still used by Android WebView in production so must
still be maintained. But most chromium developers only test on chrome.
This has already caused a bug.

Add a simple presubmit that warns when mojo files are modified, but
ipc ParamTraits files are not.

Bug: 748155
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I114d836a21ff541f38fb53012fbbeeadb3d3d46b
Reviewed-on: https://chromium-review.googlesource.com/602052
Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Bo Liu <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492357}

cc/PRESUBMIT.py

@@ -303,6 +303,25 @@ def CheckForUseOfWrongClock(input_api,
   else:
     return []
 
+def CheckIpcUpdatedWithMojo(input_api, output_api):
+  """Make sure IPC is updated whenever Mojo serialization is updated"""
+  def match_ipc(affected_file):
+    match = re.match(r'.*_param_traits.*', affected_file.LocalPath())
+    return match is not None
+
+  def match_mojo(affected_file):
+    mojo_patterns = (r'.*_struct_traits.*', r'.*\.mojom$', r'.*\.typemap$')
+    matches = (re.match(pattern, affected_file.LocalPath())
+            for pattern in mojo_patterns)
+    return any(matches)
+
+  ipc_files = input_api.AffectedFiles(file_filter=match_ipc)
+  mojo_files = input_api.AffectedFiles(file_filter=match_mojo)
+  if mojo_files and not ipc_files:
+    return [output_api.PresubmitPromptOrNotify(
+        'Make sure to update IPC ParamTraits along with mojo types.\n\n'),]
+  return []
+
 def CheckChangeOnUpload(input_api, output_api):
   results = []
   results += CheckAsserts(input_api, output_api)
@@ -315,6 +334,7 @@ def CheckChangeOnUpload(input_api, output_api):
   results += CheckNamespace(input_api, output_api)
   results += CheckForUseOfWrongClock(input_api, output_api)
   results += FindUselessIfdefs(input_api, output_api)
+  results += CheckIpcUpdatedWithMojo(input_api, output_api)
   return results
 
 def PostUploadHook(cl, change, output_api):