Disable ClangTidy namespace comments for short blocks.

Namespace comments don't assist readability for blocks that can easily
fit on a single screen.

Change-Id: I93cbebe8e51400dead794c9eb41cb1eaa86bf756
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/312639
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
diff --git a/.clang-tidy b/.clang-tidy
index 37e8152..ce6d28b 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -19,5 +19,7 @@
     readability-redundant-smartptr-get,
     readability-static-accessed-through-instance
 CheckOptions:
+  - key:             llvm-namespace-comment.ShortNamespaceLines
+    value:           40
   - key:             llvm-namespace-comment.SpacesBeforeComments
     value:           2