Back port r11886: Fix GC bug with missing handle. Bug=133618

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
===================================================================
--- src/x64/lithium-codegen-x64.cc	(revision 11886)
+++ src/x64/lithium-codegen-x64.cc	(working copy)
@@ -2218,15 +2218,15 @@
   } else {
     // Negative lookup.
     // Check prototypes.
-    HeapObject* current = HeapObject::cast((*type)->prototype());
+    Handle<HeapObject> current(HeapObject::cast((*type)->prototype()));
     Heap* heap = type->GetHeap();
-    while (current != heap->null_value()) {
-      Handle<HeapObject> link(current);
-      __ LoadHeapObject(result, link);
+    while (*current != heap->null_value()) {
+      __ LoadHeapObject(result, current);
       __ Cmp(FieldOperand(result, HeapObject::kMapOffset),
-                          Handle<Map>(JSObject::cast(current)->map()));
+                          Handle<Map>(current->map()));
       DeoptimizeIf(not_equal, env);
-      current = HeapObject::cast(current->map()->prototype());
+      current =
+          Handle<HeapObject>(HeapObject::cast(current->map()->prototype()));
     }
     __ LoadRoot(result, Heap::kUndefinedValueRootIndex);
   }