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

src/compiler/common-node-cache.cc

Index: src/compiler/common-node-cache.cc
diff --git a/src/compiler/common-node-cache.cc b/src/compiler/common-node-cache.cc
index e7f7436a0bd76624ce182e3dc4797b31b361c88a..a0ae6e8ad74e3df87e18b06cc3e74b7f0de3faee 100644
--- a/src/compiler/common-node-cache.cc
+++ b/src/compiler/common-node-cache.cc
@@ -16,6 +16,11 @@ Node** CommonNodeCache::FindExternalConstant(ExternalReference value) {
 }
 
 
+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);
@@ -23,6 +28,7 @@ void CommonNodeCache::GetCachedNodes(ZoneVector<Node*>* nodes) {
   float64_constants_.GetCachedNodes(nodes);
   external_constants_.GetCachedNodes(nodes);
   number_constants_.GetCachedNodes(nodes);
+  heap_constants_.GetCachedNodes(nodes);
 }
 
 }  // namespace compiler