Add comment to Dactyloscoper::RecordDirectSurface.

Change-Id: I711966f27f5d3b317b8ea565117fff27d863ed57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354948
Commit-Queue: Russ Hamilton <behamilton@google.com>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798813}

third_party/blink/renderer/core/frame/dactyloscoper.h

@@ -29,6 +29,8 @@ class CORE_EXPORT Dactyloscoper {
 
   static void Record(ExecutionContext*, WebFeature);
 
+  // These are helpers used by the generated bindings code when invoking IDL
+  // methods with HighEntropy=Direct.
   static void RecordDirectSurface(ExecutionContext*,
                                   WebFeature,
                                   IdentifiableToken);