[api] Allow embedder to construct an Array from Local<Value>*

Currently to obtain a v8::Array out of a C array or a std::vector,
one needs to loop through the elements and call array->Set() multiple
times, and these calls go into v8::Object::Set() which can be slow.
This patch adds a new Array::New overload that converts a
Local<Value>* with known size into a Local<Array>.

Change-Id: I0a768f0e18eec51e78d58be455482ec6425ca188
Reviewed-on: https://chromium-review.googlesource.com/c/1317049Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Cr-Commit-Position: refs/heads/master@{#57261}

include/v8.h

@@ -3677,6 +3677,12 @@ class V8_EXPORT Array : public Object {
    */
   static Local<Array> New(Isolate* isolate, int length = 0);
 
+  /**
+   * Creates a JavaScript array out of a Local<Value> array in C++
+   * with a known length.
+   */
+  static Local<Array> New(Isolate* isolate, Local<Value>* elements,
+                          size_t length);
   V8_INLINE static Array* Cast(Value* obj);
  private:
   Array();

src/api.cc

@@ -6908,6 +6908,23 @@ Local<v8::Array> v8::Array::New(Isolate* isolate, int length) {
   return Utils::ToLocal(obj);
 }
 
+Local<v8::Array> v8::Array::New(Isolate* isolate, Local<Value>* elements,
+                                size_t length) {
+  i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
+  i::Factory* factory = i_isolate->factory();
+  LOG_API(i_isolate, Array, New);
+  ENTER_V8_NO_SCRIPT_NO_EXCEPTION(i_isolate);
+  int len = static_cast<int>(length);
+
+  i::Handle<i::FixedArray> result = factory->NewFixedArray(len);
+  for (int i = 0; i < len; i++) {
+    i::Handle<i::Object> element = Utils::OpenHandle(*elements[i]);
+    result->set(i, *element);
+  }
+
+  return Utils::ToLocal(
+      factory->NewJSArrayWithElements(result, i::PACKED_ELEMENTS, len));
+}
 
 uint32_t v8::Array::Length() const {
   i::Handle<i::JSArray> obj = Utils::OpenHandle(this);

test/cctest/test-api.cc

@@ -5225,6 +5225,22 @@ THREADED_TEST(Array) {
   CHECK_EQ(27u, array->Length());
   array = v8::Array::New(context->GetIsolate(), -27);
   CHECK_EQ(0u, array->Length());
+
+  std::vector<Local<Value>> vector = {v8_num(1), v8_num(2), v8_num(3)};
+  array = v8::Array::New(context->GetIsolate(), vector.data(), vector.size());
+  CHECK_EQ(vector.size(), array->Length());
+  CHECK_EQ(1, arr->Get(context.local(), 0)
+                  .ToLocalChecked()
+                  ->Int32Value(context.local())
+                  .FromJust());
+  CHECK_EQ(2, arr->Get(context.local(), 1)
+                  .ToLocalChecked()
+                  ->Int32Value(context.local())
+                  .FromJust());
+  CHECK_EQ(3, arr->Get(context.local(), 2)
+                  .ToLocalChecked()
+                  ->Int32Value(context.local())
+                  .FromJust());
 }