Turn StoreIC::Megamorphic into a builtin, get rid of the non-monomorphic-cache

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 1c6d9f62abd2b0466467ff538367aac48a7e2aa6..592215b4839b0eb16c7d9a3683b04a421a444f5d 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -2691,10 +2691,6 @@ void Heap::CreateInitialObjects() {
   // expanding the dictionary during bootstrapping.
   set_code_stubs(*UnseededNumberDictionary::New(isolate(), 128));
 
-  // Create the non_monomorphic_cache used in stub-cache.cc. The initial size
-  // is set to avoid expanding the dictionary during bootstrapping.
-  set_non_monomorphic_cache(*UnseededNumberDictionary::New(isolate(), 64));
-
   set_instanceof_cache_function(Smi::FromInt(0));
   set_instanceof_cache_map(Smi::FromInt(0));
   set_instanceof_cache_answer(Smi::FromInt(0));
@@ -2897,7 +2893,6 @@ bool Heap::RootCanBeWrittenAfterInitialization(Heap::RootListIndex root_index) {
     case kInstanceofCacheMapRootIndex:
     case kInstanceofCacheAnswerRootIndex:
     case kCodeStubsRootIndex:
-    case kNonMonomorphicCacheRootIndex:
     case kEmptyScriptRootIndex:
     case kSymbolRegistryRootIndex:
     case kScriptListRootIndex: