[turbofan] Remove usage of Unique<T> from graph.

src/compiler/interpreter-assembler.cc

Index: src/compiler/interpreter-assembler.cc
diff --git a/src/compiler/interpreter-assembler.cc b/src/compiler/interpreter-assembler.cc
index 25d1b5eacffe1ef208e2553eef4246e1da0df9f6..6203245fb50b3f1e8f38b799cc27a796f57ce158 100644
--- a/src/compiler/interpreter-assembler.cc
+++ b/src/compiler/interpreter-assembler.cc
@@ -176,7 +176,7 @@ Node* InterpreterAssembler::NumberConstant(double value) {
 }
 
 
-Node* InterpreterAssembler::HeapConstant(Unique<HeapObject> object) {
+Node* InterpreterAssembler::HeapConstant(Handle<HeapObject> object) {
   return raw_assembler_->HeapConstant(object);
 }
 
@@ -258,8 +258,7 @@ Node* InterpreterAssembler::CallJSBuiltin(int context_index, Node* receiver,
 
 void InterpreterAssembler::Return() {
   Node* exit_trampoline_code_object =
-      HeapConstant(Unique<HeapObject>::CreateImmovable(
-          isolate()->builtins()->InterpreterExitTrampoline()));
+      HeapConstant(isolate()->builtins()->InterpreterExitTrampoline());
   // If the order of the parameters you need to change the call signature below.
   STATIC_ASSERT(0 == Linkage::kInterpreterAccumulatorParameter);
   STATIC_ASSERT(1 == Linkage::kInterpreterRegisterFileParameter);