Small DCHECK styleguide wording change.

Change the guidance for existing DCHECK code to be clearer about what to do.

Change-Id: Ica986245de4b501ee1cf332b1684b6e762a3623a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4347973
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Auto-Submit: Vincent Scheib <scheib@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Commit-Queue: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1118410}
diff --git a/styleguide/c++/c++.md b/styleguide/c++/c++.md
index 3f3fd4f0c..5ac1ebb6 100644
--- a/styleguide/c++/c++.md
+++ b/styleguide/c++/c++.md
@@ -315,8 +315,9 @@
     production, you may fall back to `DCHECK()`. Do not do this unless
     necessary.
   * Historically, Chromium code used `DCHECK()` in most cases, so a great deal
-    of existing code uses `DCHECK()` instead of `CHECK()`. You are welcome (and
-    encouraged) to migrate to `CHECK()` where the above exception is not true.
+    of existing code uses `DCHECK()` instead of `CHECK()`. You are encouraged
+    to migrate to `CHECK()` or add a comment explaining why DCHECK is
+    appropriate given the current guidance.
 
 Use `NOTREACHED_NORETURN()` to indicate a piece of code is unreachable. Control
 flow does not leave this call, so there should be no executable statements after
close