Use a dictionary-mode code cache on the map rather than a dual system.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 2140a5ed21f93ed91476d3c1d5bb28f906bee8fa..b7201295957d2cf2288b50713adae7feed46fb7d 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1486,10 +1486,6 @@ void Heap::MarkCompactPrologue() {
   CompletelyClearInstanceofCache();
 
   FlushNumberStringCache();
-  if (FLAG_cleanup_code_caches_at_gc) {
-    polymorphic_code_cache()->set_cache(undefined_value());
-  }
-
   ClearNormalizedMapCaches();
 }
 
@@ -2734,9 +2730,6 @@ void Heap::CreateInitialObjects() {
   // is set to avoid expanding the dictionary during bootstrapping.
   set_non_monomorphic_cache(*UnseededNumberDictionary::New(isolate(), 64));
 
-  set_polymorphic_code_cache(PolymorphicCodeCache::cast(
-      *factory->NewStruct(POLYMORPHIC_CODE_CACHE_TYPE)));
-
   set_instanceof_cache_function(Smi::FromInt(0));
   set_instanceof_cache_map(Smi::FromInt(0));
   set_instanceof_cache_answer(Smi::FromInt(0));
@@ -2941,7 +2934,6 @@ bool Heap::RootCanBeWrittenAfterInitialization(Heap::RootListIndex root_index) {
     case kInstanceofCacheAnswerRootIndex:
     case kCodeStubsRootIndex:
     case kNonMonomorphicCacheRootIndex:
-    case kPolymorphicCodeCacheRootIndex:
     case kEmptyScriptRootIndex:
     case kSymbolRegistryRootIndex:
     case kScriptListRootIndex: