Document when we can avoid read barriers.

Test: Rely on TreeHugger.
Bug: 119486698
Change-Id: I6d5e18709ff7d624eea7a083f39a56ed8f8ffa49
diff --git a/runtime/mirror/class-inl.h b/runtime/mirror/class-inl.h
index 2fdf69e..22597dd 100644
--- a/runtime/mirror/class-inl.h
+++ b/runtime/mirror/class-inl.h
@@ -809,8 +809,9 @@
 
 template<VerifyObjectFlags kVerifyFlags>
 inline bool Class::IsClassClass() {
-  // OK to look at from-space copies since java.lang.Class.class is not movable.
-  // See b/114413743
+  // OK to look at from-space copies since java.lang.Class.class is non-moveable
+  // (even when running without boot image, see ClassLinker::InitWithoutImage())
+  // and we're reading it for comparison only. See ReadBarrierOption.
   ObjPtr<Class> java_lang_Class = GetClass<kVerifyFlags, kWithoutReadBarrier>();
   return this == java_lang_Class;
 }