Handle Symbols in the LBranch instruction on x64.

src/code-stubs.cc

Index: src/code-stubs.cc
diff --git a/src/code-stubs.cc b/src/code-stubs.cc
index d472fa287f0c03c0a40180267b6da29828c16325..f656bf7d96b5d8e50d22a059fb5565629e374a3f 100644
--- a/src/code-stubs.cc
+++ b/src/code-stubs.cc
@@ -469,6 +469,9 @@ void CompareNilICStub::UpdateStatus(Handle<Object> object) {
 
 template<class StateType>
 void HydrogenCodeStub::TraceTransition(StateType from, StateType to) {
+  // Note: Although a no-op transition is semantically OK, it is hinting at a
+  // bug somewhere in our state transition machinery.
+  ASSERT(from != to);
   #ifdef DEBUG
   if (!FLAG_trace_ic) return;
   char buffer[100];