Improve grammar in some comments.

base/containers/small_map.h

Index: base/containers/small_map.h
diff --git a/base/containers/small_map.h b/base/containers/small_map.h
index 82ed6c5473ce7c9484534795ef0a41e674968c50..9a96f6aa93a58a319f5d707b88e5c4814d9bb9fa 100644
--- a/base/containers/small_map.h
+++ b/base/containers/small_map.h
@@ -32,7 +32,7 @@ namespace base {
 //
 //  - If you only ever keep a couple of items and have very simple usage,
 //    consider whether a using a vector and brute-force searching it will be
-//    the most efficient. It's not a lot of generated code (less then a
+//    the most efficient. It's not a lot of generated code (less than a
 //    red-black tree if your key is "weird" and not eliminated as duplicate of
 //    something else) and will probably be faster and do fewer heap allocations
 //    than std::map if you have just a couple of items.