Allow embedder to set promise internal field count

src/builtins/builtins-promise-gen.cc

 // Copyright 2016 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/builtins/builtins-promise-gen.h"
 
 #include "src/builtins/builtins-constructor-gen.h"
 #include "src/builtins/builtins-utils-gen.h"
 #include "src/builtins/builtins.h"
 #include "src/code-factory.h"
 #include "src/code-stub-assembler.h"
 #include "src/objects-inl.h"
 
 namespace v8 {
 namespace internal {
 
 using compiler::Node;
 
 Node* PromiseBuiltinsAssembler::AllocateJSPromise(Node* context) {
+  // Does this need to change to account for new internal fields?

[gsathya, 2017/05/18 16:48:33]

Nope this is fine, just the init code below.

   Node* const native_context = LoadNativeContext(context);
   Node* const promise_fun =
       LoadContextElement(native_context, Context::PROMISE_FUNCTION_INDEX);
   Node* const initial_map =
       LoadObjectField(promise_fun, JSFunction::kPrototypeOrInitialMapOffset);
   Node* const instance = AllocateJSObjectFromMap(initial_map);
   return instance;
 }
 
 void PromiseBuiltinsAssembler::PromiseInit(Node* promise) {
   StoreObjectFieldNoWriteBarrier(promise, JSPromise::kStatusOffset,
                                  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) {
   return AllocateAndInitJSPromise(context, UndefinedConstant());
 }
 
 Node* PromiseBuiltinsAssembler::AllocateAndInitJSPromise(Node* context,
                                                          Node* parent) {
   Node* const instance = AllocateJSPromise(context);
   PromiseInit(instance);
@@ skipping 1750 matching lines @@
   CSA_ASSERT(this, HasInstanceType(result_promise, JS_PROMISE_TYPE));
 
   InternalPerformPromiseThen(context, promise, resolve_reaction,
                              reject_reaction, result_promise,
                              UndefinedConstant(), UndefinedConstant());
   Return(result_promise);
 }
 
 }  // namespace internal
 }  // namespace v8