[bigint] Implement BigInt constructor.

Actually all it does is throw a TypeError.

R=jkummerow@chromium.org

Bug: v8:6791
Change-Id: I884da4eaa937519c07c3516a1713829f52e28ad8
Reviewed-on: https://chromium-review.googlesource.com/753730Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49171}

src/builtins/builtins-bigint.cc

@@ -31,19 +31,9 @@ BUILTIN(BigIntConstructor) {
 
 BUILTIN(BigIntConstructor_ConstructStub) {
   HandleScope scope(isolate);
-  Handle<Object> value = args.atOrUndefined(isolate, 1);
-  Handle<JSFunction> target = args.target();
-  Handle<JSReceiver> new_target = Handle<JSReceiver>::cast(args.new_target());
-  DCHECK(*target == target->native_context()->bigint_function());
-  Handle<JSObject> result;
-  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result,
-                                     JSObject::New(target, new_target));
-
-  // TODO(jkummerow): Implement.
-  USE(value);
-  USE(result);
-
-  UNIMPLEMENTED();
+  THROW_NEW_ERROR_RETURN_FAILURE(
+      isolate, NewTypeError(MessageTemplate::kNotConstructor,
+                            isolate->factory()->BigInt_string()));
 }
 
 BUILTIN(BigIntParseInt) {

test/mjsunit/harmony/bigint/basics.js

@@ -18,6 +18,15 @@ const six = BigInt(6);
 // BigInt
 {
   assertSame(BigInt, BigInt.prototype.constructor)
+}{
+  assertThrows(() => new BigInt, TypeError);
+  assertThrows(() => new BigInt(), TypeError);
+  assertThrows(() => new BigInt(0), TypeError);
+  assertThrows(() => new BigInt(0n), TypeError);
+  assertThrows(() => new BigInt("0"), TypeError);
+}{
+  class C extends BigInt { constructor() { throw 42 } };
+  assertThrowsEquals(() => new C, 42);
 }
 
 // ToBigInt, NumberToBigInt, BigInt