Handle external reference values properly in HConstant::ImmortalImmovable().

R=danno@chromium.org

Review URL: https://codereview.chromium.org/22274017

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16087 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.h

@@ -3212,6 +3212,9 @@ class HConstant: public HTemplateInstruction<0> {
       }
       return false;
     }
+    if (has_external_reference_value_) {
+      return false;
+    }
 
     ASSERT(!handle_.is_null());
     Heap* heap = isolate()->heap();