A64: Synchronize with r16356.

src/a64/simulator-a64.cc

Index: src/a64/simulator-a64.cc
diff --git a/src/a64/simulator-a64.cc b/src/a64/simulator-a64.cc
index 299114d224cf877f064a655822cbd521088be6f6..d2805ef58edf8a8a9ee0a4d452d04d2a9aeb2e80 100644
--- a/src/a64/simulator-a64.cc
+++ b/src/a64/simulator-a64.cc
@@ -3146,6 +3146,9 @@ void Simulator::VisitException(Instruction* instr) {
         }
 
         switch (redirection->type()) {
+          // TODO(jbramley): The old-style callbacks (returning a Handle) have
+          // been removed. We should remove their handlers from here, too.
+
           default:
             TraceSim("Type: Unknown.\n");
             UNREACHABLE();