Ensure JSProxy correctness for PrototypeIterator uses

src/ic/handler-compiler.cc

Index: src/ic/handler-compiler.cc
diff --git a/src/ic/handler-compiler.cc b/src/ic/handler-compiler.cc
index 077a3a9a6d7e2d0043291a7ee7d890e7d2079263..09ccd37bd9d17d602b373fd56cbacd4047ae1a98 100644
--- a/src/ic/handler-compiler.cc
+++ b/src/ic/handler-compiler.cc
@@ -330,6 +330,9 @@ Handle<Code> NamedLoadHandlerCompiler::CompileLoadInterceptor(
     PrototypeIterator iter(isolate(), last);
     while (!iter.IsAtEnd()) {
       lost_holder_register = true;
+      // Casting to JSObject is fine here. The LookupIterator makes sure to
+      // look behind non-masking interceptors during the original lookup, and
+      // we wouldn't try to compile a handler if there was a Proxy anywhere.
       last = iter.GetCurrent<JSObject>();
       iter.Advance();
     }