[wasm] Streaming API: own the promise.

Avoid leaking because the persistent handle isn't released. To further
clarify ownership, the v8 side owns now completely the promise.

Bug: 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: Ief9e44e60235fe6199fc4884ad1ccbd9e34cce8a
Reviewed-on: https://chromium-review.googlesource.com/591067Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46978}

include/v8.h

@@ -4165,11 +4165,14 @@ class V8_EXPORT WasmCompiledModule : public Object {
 // to simply WasmModuleObjectBuilder
 class V8_EXPORT WasmModuleObjectBuilderStreaming final {
  public:
-  WasmModuleObjectBuilderStreaming(Isolate* isolate, Local<Promise> promise);
+  WasmModuleObjectBuilderStreaming(Isolate* isolate);
   // The buffer passed into OnBytesReceived is owned by the caller.
   void OnBytesReceived(const uint8_t*, size_t size);
   void Finish();
   void Abort(Local<Value> exception);
+  Local<Promise> GetPromise();
+
+  ~WasmModuleObjectBuilderStreaming();
 
  private:
   typedef std::pair<std::unique_ptr<const uint8_t[]>, size_t> Buffer;

src/api.cc

@@ -7806,9 +7806,20 @@ MaybeLocal<WasmCompiledModule> WasmCompiledModule::Compile(Isolate* isolate,
 }
 
 WasmModuleObjectBuilderStreaming::WasmModuleObjectBuilderStreaming(
-    Isolate* isolate, Local<Promise> promise)
+    Isolate* isolate)
     : isolate_(isolate) {
-  promise_.Reset(isolate, promise);
+  MaybeLocal<Promise::Resolver> maybe_promise =
+      Promise::Resolver::New(isolate->GetCurrentContext());
+  Local<Promise::Resolver> promise;
+  if (maybe_promise.ToLocal(&promise)) {
+    promise_.Reset(isolate, promise->GetPromise());
+  } else {
+    UNREACHABLE();
+  }
+}
+
+Local<Promise> WasmModuleObjectBuilderStreaming::GetPromise() {
+  return promise_.Get(isolate_);
 }
 
 void WasmModuleObjectBuilderStreaming::OnBytesReceived(const uint8_t* bytes,
@@ -7848,6 +7859,10 @@ void WasmModuleObjectBuilderStreaming::Abort(Local<Value> exception) {
   CHECK_IMPLIES(!maybe.FromMaybe(false), i_isolate->has_scheduled_exception());
 }
 
+WasmModuleObjectBuilderStreaming::~WasmModuleObjectBuilderStreaming() {
+  promise_.Reset();
+}
+
 void WasmModuleObjectBuilder::OnBytesReceived(const uint8_t* bytes,
                                               size_t size) {
   std::unique_ptr<uint8_t[]> cloned_bytes(new uint8_t[size]);