Add a PRESUBMIT check for 'printf'.

PRESUBMIT.py

 # Copyright (c) 2013 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.
 
 """Top-level presubmit script for Blink.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
@@ skipping 215 matching lines @@
             "Source", "devtools", "scripts", "compile_frontend.py")
         out, _ = input_api.subprocess.Popen(
             [input_api.python_executable, lint_path],
             stdout=input_api.subprocess.PIPE,
             stderr=input_api.subprocess.STDOUT).communicate()
         if "WARNING" in out or "ERROR" in out:
             return [output_api.PresubmitError(out)]
     return []
 
 
+def _CheckForPrintfDebugging(input_api, output_api):
+    """Generally speaking, we'd prefer not to land patches that printf
+    debug output."""
+    os_macro_re = input_api.re.compile(r'^\s*printf\(')
+    errors = input_api.canned_checks._FindNewViolationsOfRule(
+        lambda _, x: not os_macro_re.search(x),
+        input_api, None)
+    errors = ['  * %s' % violation for violation in errors]
+    if errors:
+        return [output_api.PresubmitPromptOrNotify(
+                    'printf debugging is best debugging! That said, it might '
+                    'be a good idea to drop the following occurances from '
+                    'your patch before uploading:\n%s' % '\n'.join(errors))]
+    return []
+
+
 def CheckChangeOnUpload(input_api, output_api):
     results = []
     results.extend(_CommonChecks(input_api, output_api))
     results.extend(_CheckStyle(input_api, output_api))
+    results.extend(_CheckForPrintfDebugging(input_api, output_api))
     results.extend(_CompileDevtoolsFrontend(input_api, output_api))
     return results
 
 
 def CheckChangeOnCommit(input_api, output_api):
     results = []
     results.extend(_CommonChecks(input_api, output_api))
     results.extend(input_api.canned_checks.CheckTreeIsOpen(
         input_api, output_api,
         json_url='http://blink-status.appspot.com/current?format=json'))
     results.extend(input_api.canned_checks.CheckChangeHasDescription(
         input_api, output_api))
     results.extend(_CheckSubversionConfig(input_api, output_api))
     return results
 
 def GetPreferredTrySlaves(project, change):
     return ['linux_blink_rel', 'mac_blink_rel', 'win_blink_rel']