Allow NOLINT to skip the std::abs PRESUBMIT check.

cc/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 cc.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts for
 details on the presubmit API built into gcl.
 """
 
@@ skipping 56 matching lines @@
   using_std_abs_files = []
   found_fabs_files = []
   missing_std_prefix_files = []
 
   for f in input_api.AffectedSourceFiles(source_file_filter):
     contents = input_api.ReadFile(f, 'rb')
     if re.search(r"using std::f?abs;", contents):
       using_std_abs_files.append(f.LocalPath())
     if re.search(r"\bfabsf?\(", contents):
       found_fabs_files.append(f.LocalPath());
-    # The following regular expression in words says:
-    # "if there is no 'std::' behind an 'abs(' or 'absf(',
-    # or if there is no 'std::' behind a 'fabs(' or 'fabsf(',
-    # then it's a match."
-    if re.search(r"((?<!std::)(\babsf?\()|(?<!std::)(\bfabsf?\())", contents):
+
+    no_std_prefix = r"(?<!std::)"
+    # Matches occurrences of abs/absf/fabs/fabsf without a "std::" prefix.
+    abs_without_prefix = r"%s(\babsf?\()" % no_std_prefix
+    fabs_without_prefix = r"%s(\bfabsf?\()" % no_std_prefix
+    # Skips matching any lines that have "// NOLINT".
+    no_nolint = r"(?![^\n]*//\s+NOLINT)"
+
+    expression = re.compile("(%s|%s)%s" %
+        (abs_without_prefix, fabs_without_prefix, no_nolint))
+    if expression.search(contents):
       missing_std_prefix_files.append(f.LocalPath())
 
   result = []
   if using_std_abs_files:
     result.append(output_api.PresubmitError(
         'These files have "using std::abs" which is not permitted.',
         items=using_std_abs_files))
   if found_fabs_files:
     result.append(output_api.PresubmitError(
         'std::abs() should be used instead of std::fabs() for consistency.',
@@ skipping 92 matching lines @@
   results += CheckSpamLogging(input_api, output_api, black_list=CC_PERF_TEST)
   results += CheckPassByValue(input_api, output_api)
   results += CheckChangeLintsClean(input_api, output_api)
   results += CheckTodos(input_api, output_api)
   return results
 
 def GetPreferredTrySlaves(project, change):
   return [
     'linux_layout_rel',
     ]