Remove IsPromise brand check.

Fixes #41.

index.html

@@ -2148,7 +2148,7 @@
 		</div>
 	</div>
 	<div id="spec-container">
-		<h1 class="version first">Stage 3 Draft / October 27, 2017</h1>
+		<h1 class="version first">Stage 3 Draft / October 30, 2017</h1>
 		<h1 class="title">Promise.prototype.finally</h1>
 
 		<emu-clause id="sec-promise.prototype.finally">
@@ -2159,8 +2159,7 @@ <h1><span class="secnum">1</span>Promise.prototype.finally ( <var>onFinally</var
 					<li>Let <var>promise</var> be the
 						<emu-val>this</emu-val> value.</li>
 					<li>If
-						<emu-xref aoid="IsPromise" id="_ref_2"><a href="https://tc39.github.io/ecma262/#sec-ispromise">IsPromise</a></emu-xref>(<var>promise</var>) is
-						<emu-val>false</emu-val>, throw a
+						<emu-xref aoid="Type" id="_ref_2"><a href="https://tc39.github.io/ecma262/#sec-ecmascript-data-types-and-values">Type</a></emu-xref>(<var>promise</var>) is not Object, throw a
 						<emu-val>TypeError</emu-val> exception.</li>
 					<li>Let <var>C</var> be ?
 						<emu-xref aoid="SpeciesConstructor" id="_ref_3"><a href="https://tc39.github.io/ecma262/#sec-speciesconstructor">SpeciesConstructor</a></emu-xref>(<var>promise</var>,

polyfill.js

@@ -26,14 +26,17 @@ if (typeof Promise.prototype.finally !== 'function') {
 
 	var shim = {
 		finally(onFinally) {
+			var promise = this;
+			if (typeof promise !== 'object' || promise === null) {
+				throw new TypeError('"this" value is not an Object');
+			}
+			var C = speciesConstructor(promise, Promise); // throws if SpeciesConstructor throws
 			var handler = typeof onFinally === 'function' ? onFinally : () => {};
-			var C;
 			var newPromise = Promise.prototype.then.call(
-				this, // throw if IsPromise(this) is not true
+				promise,
 				x => new C(resolve => resolve(handler())).then(() => x),
 				e => new C(resolve => resolve(handler())).then(() => { throw e; })
 			);
-			C = speciesConstructor(this, Promise); // throws if SpeciesConstructor throws
 			return newPromise;
 		}
 	};

spec.emu

@@ -14,7 +14,7 @@ contributors: Jordan Harband
 	<p>When the `finally` method is called with argument _onFinally_, the following steps are taken:</p>
 	<emu-alg>
 		1. Let _promise_ be the *this* value.
-		1. If IsPromise(_promise_) is *false*, throw a *TypeError* exception.
+		1. If Type(_promise_) is not Object, throw a *TypeError* exception.
 		1. Let _C_ be ? SpeciesConstructor(_promise_, %Promise%).
 		1. Assert: IsConstructor(_C_) is *true*.
 		1. If IsCallable(_onFinally_) is not *true*,

spec.md

@@ -2,7 +2,7 @@
 
 When the `finally` method is called with argument _onFinally_, the following steps are taken:
   1. Let _promise_ be the **this** value.
-  1. If <a href="http://www.ecma-international.org/ecma-262/6.0/index.html#sec-ispromise">IsPromise</a>(_promise_) is **false**, throw a **TypeError** exception.
+  1. If <a href="https://tc39.github.io/ecma262/#sec-ecmascript-data-types-and-values">Type</a>(_promise_) is not Object, throw a *TypeError* exception.
   1. Assert: <a href="https://tc39.github.io/ecma262/#sec-isconstructor">IsConstructor</a>(_C_) is *true*.
     1. If <a href="https://tc39.github.io/ecma262/#sec-iscallable">IsCallable</a>(_onFinally_) is not *true*,
       1. Let _thenFinally_ be _onFinally_.
@@ -46,14 +46,14 @@ When a CatchFinally function _F_ is called with argument _reason_, the following
 
 The `resolve` function returns either a new promise resolved with the passed argument, or the argument itself if the argument is a promise produced by this constructor.
   1. Let _C_ be the *this* value.
-  1. If <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-ecmascript-data-types-and-values">Type</a>(_C_) is not Object, throw a *TypeError* exception.
+  1. If <a href="https://tc39.github.io/ecma262/#sec-ecmascript-data-types-and-values">Type</a>(_C_) is not Object, throw a *TypeError* exception.
   1. Return ? PromiseResolve(_C_, _x_).
 
 Note: the `resolve` function expects its *this* value to be a constructor function that supports the parameter conventions of the `Promise` constructor.
 
 ## PromiseResolve ( _C_, _x_ )
 The abstract operation PromiseResolve, given a constructor and a value, returns a new promise resolved with that value.
-  1. Assert: <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-ecmascript-data-types-and-values">Type</a>(_C_) is Object.
+  1. Assert: <a href="https://tc39.github.io/ecma262/#sec-ecmascript-data-types-and-values">Type</a>(_C_) is Object.
   1. If <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-ispromise">IsPromise</a>(_x_) is *true*, then
     1. Let _xConstructor_ be ? <a href="http://www.ecma-international.org/ecma-262/6.0/#sec-get-o-p">Get</a>(_x_, `"constructor"`).
     1. If SameValue(_xConstructor_, _C_) is *true*, return _x_.