Add a presubmit check that warns about declaring Singleton<T> in header files

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.
 
 """Top-level presubmit script for Chromium.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into depot_tools.
 """
 
@@ skipping 1287 matching lines @@
     sys.path = sys.path + [input_api.os_path.join(
         input_api.PresubmitLocalPath(), 'android_webview', 'tools')]
     import copyright_scanner
   finally:
     # Restore sys.path to what it was before.
     sys.path = original_sys_path
 
   return copyright_scanner.ScanAtPresubmit(input_api, output_api)
 
 
+def _CheckSingletonInHeaders(input_api, output_api):
+  """Checks to make sure no header files have |Singleton<|."""
+  def FileFilter(affected_file):
+    # It's ok for base/memory/singleton.h to have |Singleton<|.
+    black_list = (_EXCLUDED_PATHS +
+                  input_api.DEFAULT_BLACK_LIST +
+                  (r"^base[\\\/]memory[\\\/]singleton\.h$",))
+    return input_api.FilterSourceFile(affected_file, black_list=black_list)
+
+  pattern = input_api.re.compile(r'(?<!class\s)Singleton\s*<')
+  files = []
+  for f in input_api.AffectedSourceFiles(FileFilter):
+    if (f.LocalPath().endswith('.h') or f.LocalPath().endswith('.hxx') or
+        f.LocalPath().endswith('.hpp') or f.LocalPath().endswith('.inl')):
+      contents = input_api.ReadFile(f.LocalPath())
+      for line in contents.splitlines(False):
+        if (not input_api.re.match(r'//', line) and # Strip C++ comment.
+            pattern.search(line)):
+          files.append(f)
+          break
+
+  if files:
+    return [ output_api.PresubmitError(
+        'Found Singleton<T> in the following header files.\n' +
+        'Please move them to an appropriate source file so that the ' +
+        'template gets instantiated in a single compilation unit.',
+        files) ]
+  return []
+
+
 _DEPRECATED_CSS = [
   # Values
   ( "-webkit-box", "flex" ),
   ( "-webkit-inline-box", "inline-flex" ),
   ( "-webkit-flex", "flex" ),
   ( "-webkit-inline-flex", "inline-flex" ),
   ( "-webkit-min-content", "min-content" ),
   ( "-webkit-max-content", "max-content" ),
 
   # Properties
@@ skipping 97 matching lines @@
   results.extend(_CheckSpamLogging(input_api, output_api))
   results.extend(_CheckForAnonymousVariables(input_api, output_api))
   results.extend(_CheckCygwinShell(input_api, output_api))
   results.extend(_CheckUserActionUpdate(input_api, output_api))
   results.extend(_CheckNoDeprecatedCSS(input_api, output_api))
   results.extend(_CheckNoDeprecatedJS(input_api, output_api))
   results.extend(_CheckParseErrors(input_api, output_api))
   results.extend(_CheckForIPCRules(input_api, output_api))
   results.extend(_CheckForCopyrightedCode(input_api, output_api))
   results.extend(_CheckForWindowsLineEndings(input_api, output_api))
+  results.extend(_CheckSingletonInHeaders(input_api, output_api))
 
   if any('PRESUBMIT.py' == f.LocalPath() for f in input_api.AffectedFiles()):
     results.extend(input_api.canned_checks.RunUnitTestsInDirectory(
         input_api, output_api,
         input_api.PresubmitLocalPath(),
         whitelist=[r'^PRESUBMIT_test\.py$']))
   return results
 
 
 def _CheckAuthorizedAuthor(input_api, output_api):
@@ skipping 322 matching lines @@
         if 'presubmit' in builder:
           builders[master].pop(builder)
 
   # Match things like path/aura/file.cc and path/file_aura.cc.
   # Same for chromeos.
   if any(re.search(r'[\\\/_](aura|chromeos)', f) for f in files):
     tryserver_linux = builders.setdefault('tryserver.chromium.linux', {})
     tryserver_linux['linux_chromium_chromeos_asan_rel_ng'] = ['defaulttests']
 
   return builders