[cpplint] Fix regexp for class decorators

This also allows digits in class decorators, to also match macros like
V8_EXPORT_PRIVATE.

Note: I uploaded a pull request for the (previous) upstream at
https://github.com/google/styleguide/pull/422, but then was told that
that repository is not maintained any more.

R=jochen@chromium.org

Bug: chromium:916550

Change-Id: I24cd1829b794b296be8e0c2829271c746751ee1c
Reviewed-on: https://chromium-review.googlesource.com/c/1383472
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>

README.md

@@ -67,5 +67,8 @@ See also [open bugs](https://bugs.chromium.org/p/chromium/issues/list?can=2&q=co
 
 ### cpplint.py
 
-To update cpplint.py, please submit the change upstream first at
-https://github.com/google/styleguide/tree/gh-pages/cpplint then copy it down.
+Until 2018, our `cpplint.py` was a copy of the upstream version at
+https://github.com/google/styleguide/tree/gh-pages/cpplint. Unfortunately, that
+repository is not maintained any more.
+If you want to update `cpplint.py` in `depot_tools`, just upload a patch to do
+so. We will figure out a long-term strategy via issue https://crbug.com/916550.

cpplint.py

@@ -2530,7 +2530,7 @@ class NestingState(object):
     #   };
     class_decl_match = Match(
         r'^(\s*(?:template\s*<[\w\s<>,:]*>\s*)?'
-        r'(class|struct)\s+(?:[A-Z_]+\s+)*(\w+(?:::\w+)*))'
+        r'(class|struct)\s+(?:[A-Z0-9_]+\s+)*(\w+(?:::\w+)*))'
         r'(.*)$', line)
     if (class_decl_match and
         (not self.stack or self.stack[-1].open_parentheses == 0)):