[PPAPI] Make the NaCl SDK presubmit check a warning instead of an error.

ppapi/PRESUBMIT.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import os
 import re
 import sys
 import subprocess
 
 
-def RunCmdAndCheck(cmd, err_string, output_api, cwd=None):
+def RunCmdAndCheck(cmd, err_string, output_api, cwd=None, warning=False):
   results = []
   p = subprocess.Popen(cmd, cwd=cwd,
                        stdout=subprocess.PIPE,
                        stderr=subprocess.PIPE)
   (p_stdout, p_stderr) = p.communicate()
   if p.returncode:
-    results.append(
-        output_api.PresubmitError(err_string,
-                                  long_text=p_stderr))
+    if warning:
+      results.append(output_api.PresubmitPromptWarning(
+        '%s\n\n%s' % (err_string, p_stderr)))
+    else:
+      results.append(
+          output_api.PresubmitError(err_string,
+                                    long_text=p_stderr))
   return results
 
 
 def RunUnittests(input_api, output_api):
   # Run some Generator unittests if the generator source was changed.
   results = []
   files = input_api.LocalPaths()
   generator_files = []
   for filename in files:
     name_parts = filename.split(os.sep)
@@ skipping 103 matching lines @@
       nacl_sdk_files.append(filename)
 
   if not nacl_sdk_files:
     return []
 
   verify_ppapi_py = os.path.join(input_api.change.RepositoryRoot(),
                                  'native_client_sdk', 'src', 'build_tools',
                                  'verify_ppapi.py')
   cmd = [sys.executable, verify_ppapi_py] + nacl_sdk_files
   return RunCmdAndCheck(cmd,
-                        'PPAPI Interface modified without updating NaCl SDK.',
-                        output_api)
+                        'PPAPI Interface modified without updating NaCl SDK.\n'
+                        '(note that some dev interfaces should not be added '
+                        'the NaCl SDK; when in doubt, ask a ppapi OWNER.)',
+                        output_api,
+                        warning=True)
 
 # Verify that changes to ppapi/thunk/interfaces_* files have a corresponding
 # change to tools/metrics/histograms/histograms.xml for UMA tracking.
 def CheckHistogramXml(input_api, output_api):
   # We can't use input_api.LocalPaths() here because we need to know about
   # changes outside of ppapi/. See tools/depot_tools/presubmit_support.py for
   # details on input_api.
   files = input_api.change.AffectedFiles()
 
   INTERFACE_FILES = ('ppapi/thunk/interfaces_legacy.h',
@@ skipping 171 matching lines @@
 
   return results
 
 
 def CheckChangeOnUpload(input_api, output_api):
   return CheckChange(input_api, output_api)
 
 
 def CheckChangeOnCommit(input_api, output_api):
   return CheckChange(input_api, output_api)