Add markPromiseAsHandled V8 extra util

This will allow V8 extra consumers to mark a promise as handled without
adding redundant empty onRejected handlers. This is needed by streams as
discussed in https://github.com/whatwg/streams/issues/547.

BUG=chromium:654701

Review-Url: https://codereview.chromium.org/2498143002
Cr-Commit-Position: refs/heads/master@{#41012}

src/js/promise.js

@@ -587,6 +587,10 @@ function PromiseHasUserDefinedRejectHandler() {
   return PromiseHasUserDefinedRejectHandlerRecursive(this);
 };
 
+function MarkPromiseAsHandled(promise) {
+  SET_PRIVATE(promise, promiseHasHandlerSymbol, true);
+}
+
 
 function PromiseSpecies() {
   return this;
@@ -632,7 +636,8 @@ utils.InstallFunctions(GlobalPromise.prototype, DONT_ENUM, [
 utils.InstallFunctions(extrasUtils, 0, [
   "createPromise", PromiseCreate,
   "resolvePromise", ResolvePromise,
-  "rejectPromise", DoRejectPromise
+  "rejectPromise", DoRejectPromise,
+  "markPromiseAsHandled", MarkPromiseAsHandled
 ]);
 
 utils.Export(function(to) {

test/cctest/test-api.cc

@@ -25396,6 +25396,12 @@ TEST(ExtrasUtilsObject) {
   rejected_promise->Catch(env.local(), store).ToLocalChecked();
   isolate->RunMicrotasks();
   CHECK_EQ(3, CompileRun("result")->Int32Value(env.local()).FromJust());
+
+  auto rejected_but_handled_promise =
+      result->Get(env.local(), v8_str("rejectedButHandledPromise"))
+          .ToLocalChecked()
+          .As<v8::Promise>();
+  CHECK_EQ(true, rejected_but_handled_promise->HasHandler());
 }
 
 

test/cctest/test-extra.js

@@ -65,11 +65,16 @@
       return (arg1 === arg2 && arg2 === 'x') ? 3 : -1;
     }, null, new v8.InternalPackedArray('x', 'x')));
 
+    const rejectedButHandledPromise = v8.createPromise();
+    v8.rejectPromise(rejectedButHandledPromise, 4);
+    v8.markPromiseAsHandled(rejectedButHandledPromise);
+
     return {
       privateSymbol: v8.createPrivateSymbol('sym'),
       fulfilledPromise, // should be fulfilled with 1
       fulfilledPromise2, // should be fulfilled with 2
-      rejectedPromise // should be rejected with 3
+      rejectedPromise, // should be rejected with 3
+      rejectedButHandledPromise // should be rejected but have a handler
     };
   };
 })