Allow embedder to set promise internal field count

src/builtins/builtins-promise-gen.cc

Index: src/builtins/builtins-promise-gen.cc
diff --git a/src/builtins/builtins-promise-gen.cc b/src/builtins/builtins-promise-gen.cc
index a050f18d668a4b591ef78a4766504f7cc7208ba3..b1412eb7cd5f81a889761541ca8efaac7429e7e9 100644
--- a/src/builtins/builtins-promise-gen.cc
+++ b/src/builtins/builtins-promise-gen.cc
@@ -31,6 +31,10 @@ void PromiseBuiltinsAssembler::PromiseInit(Node* promise) {
                                  SmiConstant(v8::Promise::kPending));
   StoreObjectFieldNoWriteBarrier(promise, JSPromise::kFlagsOffset,
                                  SmiConstant(0));
+  for (int i = 0; i < v8::Promise::kEmbedderFieldCount; i++) {
+    int offset = JSPromise::kSize + i * kPointerSize;
+    StoreObjectFieldNoWriteBarrier(promise, offset, SmiConstant(Smi::kZero));
+  }
 }
 
 Node* PromiseBuiltinsAssembler::AllocateAndInitJSPromise(Node* context) {
@@ -62,6 +66,10 @@ Node* PromiseBuiltinsAssembler::AllocateAndSetJSPromise(Node* context,
   StoreObjectFieldNoWriteBarrier(instance, JSPromise::kResultOffset, result);
   StoreObjectFieldNoWriteBarrier(instance, JSPromise::kFlagsOffset,
                                  SmiConstant(0));
+  for (int i = 0; i < v8::Promise::kEmbedderFieldCount; i++) {
+    int offset = JSPromise::kSize + i * kPointerSize;
+    StoreObjectFieldNoWriteBarrier(instance, offset, SmiConstant(Smi::kZero));
+  }
 
   Label out(this);
   GotoIfNot(IsPromiseHookEnabledOrDebugIsActive(), &out);