Use v8::Promise::Then in ScriptPromise::then.

ScriptPromise::then should use v8::Promise::Then in order to handle
multiply-wrapped Promises correctly.

BUG=371288

Review URL: https://codereview.chromium.org/316453002

git-svn-id: svn://svn.chromium.org/blink/trunk@176194 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/fast/js/Promise-native-then.html

@@ -28,7 +28,7 @@ newPromise.then(function(result) {
     testFailed("rejected");
 }).then(finishJSTest, finishJSTest);
 
-resolve(10);
+resolve(new Promise(function(resolve) { resolve(10); }));
 
 </script>
 </body>

third_party/WebKit/Source/bindings/v8/ScriptPromise.cpp

@@ -79,11 +79,10 @@ ScriptPromise ScriptPromise::then(PassOwnPtr<ScriptFunction> onFulfilled, PassOw
     // In fact it is not the exact bahavior of Promise.prototype.then
     // but that is not a problem in this case.
     v8::Local<v8::Promise> resultPromise = promise.As<v8::Promise>();
-    // FIXME: Use Then once it is introduced.
     if (!v8OnFulfilled.IsEmpty()) {
-        resultPromise = resultPromise->Chain(v8OnFulfilled);
+        resultPromise = resultPromise->Then(v8OnFulfilled);
         if (resultPromise.IsEmpty()) {
-            // v8::Promise::Chain may return an empty value, for example when
+            // v8::Promise::Then may return an empty value, for example when
             // the stack is exhausted.
             return ScriptPromise();
         }