[promise] Remove IsPromise brand check in PromiseFinally

The IsPromise brand check is now replaced with an IsObject check.

The spec was changed here:
https://github.com/tc39/proposal-promise-finally/commit/a1628886f85a897df5cd967ea36f025e8f89cb7a

Bug: v8:7095
Change-Id: I5668083c888f9efcdfc1491c919c810c75d73ac7
Reviewed-on: https://chromium-review.googlesource.com/826606Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50108}

src/builtins/builtins-promise-gen.cc

@@ -1683,9 +1683,9 @@ TF_BUILTIN(PromiseFinally, PromiseBuiltinsAssembler) {
   Node* const on_finally = Parameter(Descriptor::kOnFinally);
   Node* const context = Parameter(Descriptor::kContext);
 
-  // 2. If IsPromise(promise) is false, throw a TypeError exception.
-  ThrowIfNotInstanceType(context, promise, JS_PROMISE_TYPE,
-                         "Promise.prototype.finally");
+  // 2. If Type(promise) is not Object, throw a TypeError exception.
+  ThrowIfNotJSReceiver(context, promise, MessageTemplate::kCalledOnNonObject,
+                       "Promise.prototype.finally");
 
   // 3. Let C be ? SpeciesConstructor(promise, %Promise%).
   Node* const native_context = LoadNativeContext(context);

test/mjsunit/harmony/promise-prototype-finally.js

@@ -605,3 +605,13 @@ testAsync(assert => {
     .then(() => assert.equals(1, value));
 
 }, "PromiseResolve-ordering");
+
+(function testIsObject() {
+  var called = false;
+  var p = new Proxy(Promise.resolve(), {});
+  var oldThen = Promise.prototype.then;
+  Promise.prototype.then = () => called = true;
+  Promise.prototype.finally.call(p);
+  assertTrue(called);
+  Promise.prototype.then = oldThen;
+})();