Add TypeTraits template for checking safe bitfields (WIP)

third_party/WebKit/Tools/Scripts/webkitpy/style/checkers/cpp.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/style/checkers/cpp.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/style/checkers/cpp.py b/third_party/WebKit/Tools/Scripts/webkitpy/style/checkers/cpp.py
index c5fda9168636112c7124549b5cda3057896c9446..cfe3302ec2ea733a1ea9e6d26183ecc1d7422368 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/style/checkers/cpp.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/style/checkers/cpp.py
@@ -1493,10 +1493,22 @@ def check_for_non_standard_constructs(clean_lines, line_number,
             classinfo.name.startswith('Expected')):
         args = match(r'\s*(\S+)\s+(\S+)\s*:\s*\d+\s*;', line)
         if args:
-            error(line_number, 'runtime/bitfields', 4,
-                  'Member %s of class %s defined as a bitfield of type %s. '
-                  'Please declare all bitfields as unsigned.'
-                  % (args.group(2), classinfo.name, args.group(1)))
+            field_type = args.group(1)
+            field_name = args.group(2)
+
+            # Look for an unsigned assert for this type in this file.
+            has_assert = False
+            for other_line in clean_lines.lines:
+                if match(r'\bstatic_assert(\s*IsEnumSafeToStoreInBitfield\s*<\s*(\S+)?' + field_type + r'>::value\s*);', other_line):
+                    has_assert = True
+                    break
+
+            if not has_assert:
+                error(line_number, 'runtime/bitfields', 4,
+                      'Member %s of class %s defined as a bitfield of type %s. '
+                      'Please declare all bitfields as unsigned, or add '
+                      'static_assert(IsEnumSafeToStoreInBitfield<%s>::value).'
+                      % (field_name, classinfo.name, field_type, field_type))
 
 
 def check_spacing_for_function_call(line, line_number, error):