Adds PRESUBMIT.py check to look for unprefixed string16.

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index e4db30215d9063d9874a696a26c4516e4f8c8738..bd31ff1673d17e9d8b5ec8e9d69c4545d1ceb48e 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -1026,6 +1026,7 @@ def _CommonChecks(input_api, output_api):
   results.extend(_CheckForAnonymousVariables(input_api, output_api))
   results.extend(_CheckCygwinShell(input_api, output_api))
   results.extend(_CheckJavaStyle(input_api, output_api))
+  results.extend(_CheckForString16(input_api, output_api))
 
   if any('PRESUBMIT.py' == f.LocalPath() for f in input_api.AffectedFiles()):
     results.extend(input_api.canned_checks.RunUnitTestsInDirectory(
@@ -1168,6 +1169,35 @@ def _CheckForInvalidOSMacros(input_api, output_api):
       'or add your macro to src/PRESUBMIT.py.', bad_macros)]
 
 
+def _CheckForString16InFile(input_api, f):
+  """Check for string16 without base:: in front."""
+  reg = input_api.re.compile(r'\b(?<!base::)string16\b')
+  use = 'using base::string16;'
+  include = '#include "base/strings/string16.h"'
+  results = []
+  for lnum, line in f.ChangedContents():
+    if reg.search(line) and not include in line and not use in f.NewContents():
+      results.append('    %s:%d' % (f.LocalPath(), lnum))
+  return results
+
+
+def _CheckForString16(input_api, output_api):
+  file_filter = lambda f: input_api.FilterSourceFile(f,
+      white_list=(r'^chrome[\\\/]browser[\\\/]', ),
+      black_list=(_EXCLUDED_PATHS + _TEST_CODE_EXCLUDED_PATHS +
+                  input_api.DEFAULT_BLACK_LIST))
+
+  unprefixed = []
+  for f in input_api.AffectedFiles(file_filter=file_filter):
+    unprefixed.extend(_CheckForString16InFile(input_api, f))
+
+  if not unprefixed:
+    return []
+
+  return [output_api.PresubmitPromptWarning(
+      'string16 should be prefixed with base:: namespace.', unprefixed)]
+
+
 def CheckChangeOnUpload(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))