PRESUBMIT: Improve error message about checkdeps.

PRESUBMIT.py

 # Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import json
 import os
@@ skipping 380 matching lines @@
       added_includes):
     description_with_path = '%s\n    %s' % (path, rule_description)
     if rule_type == Rule.DISALLOW:
       error_descriptions.append(description_with_path)
     else:
       warning_descriptions.append(description_with_path)
 
   results = []
   if error_descriptions:
     results.append(output_api.PresubmitError(
-        'You added one or more #includes that violate checkdeps rules.',
+        'You added one or more #includes that violate checkdeps rules.\n'
+        'Check that the DEPS files in these locations contain valid rules.\n'
+        'See https://cs.chromium.org/chromium/src/buildtools/checkdeps/ for '
+        'more details about checkdeps.',
         error_descriptions))
   if warning_descriptions:
     results.append(output_api.PresubmitPromptOrNotify(
         'You added one or more #includes of files that are temporarily\n'
         'allowed but being removed. Can you avoid introducing the\n'
-        '#include? See relevant DEPS file(s) for details and contacts.',
+        '#include? See relevant DEPS file(s) for details and contacts.\n'
+        'See https://cs.chromium.org/chromium/src/buildtools/checkdeps/ for '
+        'more details about checkdeps.',
         warning_descriptions))
   return results
 
 def _CheckChangeHasBugField(input_api, output_api):
   """Requires that the changelist have a BUG= field.
 
   This check is stricter than the one in depot_tools/presubmit_canned_checks.py
   since it fails the presubmit if the BUG= field is missing or doesn't contain
   a bug reference.
   """
@@ skipping 141 matching lines @@
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   results.extend(_CheckChangeHasBugField(input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasTestField(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckTreeIsOpen(
       input_api, output_api,
       json_url='http://webrtc-status.appspot.com/current?format=json'))
   return results