[await] Add async iterator tests for await optimization

These tests make sure the ticks are correct when resolving against a
Promise.

Without the optimization, the result is:
"start,tick 1,tick 2,tick 3,tick 4,done,tick 5"

With the optimization, the result is:
"start,tick 1,tick 2,done,tick 3,tick 4,tick 5"

Bug: v8:8267
Change-Id: I6c6499c7c256927531a99bab4ae1c5bd5069ef7c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1534884
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60615}

test/mjsunit/harmony/async-from-sync-iterator-next-tick-count.js

@@ -0,0 +1,33 @@
+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Flags: --allow-natives-syntax
+
+const actual = [];
+
+function createIterator() {
+  return {
+    [Symbol.iterator]() { return this; },
+
+    next() {
+      return { value: Promise.resolve(1), done: true};
+    }
+  };
+}
+
+actual.push("start");
+iter = %CreateAsyncFromSyncIterator(createIterator());
+
+Promise.resolve(0)
+  .then(() => actual.push("tick 1"))
+  .then(() => actual.push("tick 2"))
+  .then(() => actual.push("tick 3"))
+  .then(() => actual.push("tick 4"))
+  .then(() => actual.push("tick 5"));
+
+let p = iter.next();
+p.then(_ => { actual.push("done"); } );
+
+%PerformMicrotaskCheckpoint();
+assertSame("start,tick 1,tick 2,done,tick 3,tick 4,tick 5", actual.join(","))

test/mjsunit/harmony/async-from-sync-iterator-return-tick-count.js

@@ -0,0 +1,33 @@
+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Flags: --allow-natives-syntax
+
+const actual = [];
+
+function createIterator() {
+  return {
+    [Symbol.iterator]() { return this; },
+
+    return() {
+      return { value: Promise.resolve(1), done: true};
+    }
+  };
+}
+
+actual.push("start");
+iter = %CreateAsyncFromSyncIterator(createIterator());
+
+Promise.resolve(0)
+  .then(() => actual.push("tick 1"))
+  .then(() => actual.push("tick 2"))
+  .then(() => actual.push("tick 3"))
+  .then(() => actual.push("tick 4"))
+  .then(() => actual.push("tick 5"));
+
+let p = iter.return();
+p.then(_ => { actual.push("done"); } );
+
+%PerformMicrotaskCheckpoint();
+assertSame("start,tick 1,tick 2,done,tick 3,tick 4,tick 5", actual.join(","))

test/mjsunit/harmony/async-from-sync-iterator-throw-tick-count.js

@@ -0,0 +1,33 @@
+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Flags: --allow-natives-syntax
+
+const actual = [];
+
+function createIterator() {
+  return {
+    [Symbol.iterator]() { return this; },
+
+    throw() {
+      return { value: Promise.resolve(1), done: true};
+    }
+  };
+}
+
+actual.push("start");
+iter = %CreateAsyncFromSyncIterator(createIterator());
+
+Promise.resolve(0)
+  .then(() => actual.push("tick 1"))
+  .then(() => actual.push("tick 2"))
+  .then(() => actual.push("tick 3"))
+  .then(() => actual.push("tick 4"))
+  .then(() => actual.push("tick 5"));
+
+let p = iter.throw();
+p.then(_ => { actual.push("done"); } );
+
+%PerformMicrotaskCheckpoint();
+assertSame("start,tick 1,tick 2,done,tick 3,tick 4,tick 5", actual.join(","))