[debugger] add test case for debug-evaluation with promise microtasks.

test/mjsunit/es6/debug-promises/evaluate-across-microtasks.js

+// Copyright 2014 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: --expose-debug-as debug
+
+var Debug = debug.Debug;
+var listenerComplete = false;
+var exception = null;
+var count = 0;
+var log = [];
+
+function LogX(x) {
+  var stored_count = count;
+  return function() {
+    log.push(`[${stored_count}] ${x}`);
+  };
+}
+
+var expectation = [ "[0] debugger", "[1] start", "[1] then 1", "[1] then 2",
+                    "[1] then 3", "[1] debugger", "[2] then 1", "[2] then 2",
+                    "[1] catch", "[2] then 3", "[2] debugger", "[3] then 1",
+                    "[3] then 2", "[2] catch", "[3] then 3", "[3] debugger" ];
+
+function DebuggerStatement() {
+  log.push(`[${count}] debugger`);
+  if (count++ < 3) {
+    debugger;
+  } else {
+    try {

[caitp (gmail), 2016/05/31 11:44:32]

I think we hit this because d8 won't die if the microtask queue is non-empty,
right? But it's not really asserted that this assertion is ever reached, so it's
possible it could fail silently.

Is there a way we can ensure (and assert) that this line is reached before
quitting?

[Yang, 2016/06/01 08:55:21]

Good point. I haven't found a good way to do this than adding a repeating micro
tasks that polls whether we hit this line.

[Dan Ehrenberg, 2016/06/01 10:38:13]

Maybe you could use the new %RunMicrotasks call, which should keep going until
the microtask queue is exhausted.

+      assertEquals(expectation, log);
+    } catch (e) {
+      print(e, e.stack);
+      quit(1);
+    }
+  }
+}
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    var p = Promise.resolve();
+    var q = p.then(LogX("then 1"));
+    p.then(LogX("then 2"));
+    q.then(LogX("then 3"));
+    q.then(DebuggerStatement);
+    var r = q.then(() => { throw 1; });
+    r.catch(LogX("catch"));
+    listenerComplete = true;
+  } catch (e) {
+    exception = e;
+    print("failure");

[caitp (gmail), 2016/05/31 11:44:32]

if we fail here, it would be helpful to print the exception

[Yang, 2016/06/01 08:55:21]

Done.

+    quit(1);
+  };
+};
+
+// Add the debug event listener.
+Debug.setListener(listener);
+
+DebuggerStatement();
+LogX("start")();
+
+// Make sure that the debug event listener was invoked.
+assertTrue(listenerComplete);