[turbofan] Implement proper caching of heap constants in the JSGraph.

src/compiler/common-node-cache.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/common-node-cache.h"
 
 #include "src/assembler.h"
 #include "src/compiler/node.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 Node** CommonNodeCache::FindExternalConstant(ExternalReference value) {
   return external_constants_.Find(zone(), bit_cast<intptr_t>(value.address()));
 }
 
 
+Node** CommonNodeCache::FindHeapConstant(Handle<HeapObject> value) {
+  return heap_constants_.Find(zone(), bit_cast<intptr_t>(value.location()));
+}
+
+
 void CommonNodeCache::GetCachedNodes(ZoneVector<Node*>* nodes) {
   int32_constants_.GetCachedNodes(nodes);
   int64_constants_.GetCachedNodes(nodes);
   float32_constants_.GetCachedNodes(nodes);
   float64_constants_.GetCachedNodes(nodes);
   external_constants_.GetCachedNodes(nodes);
   number_constants_.GetCachedNodes(nodes);
+  heap_constants_.GetCachedNodes(nodes);
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8