Do not trigger ExceptionEvents for another forwarding case

test/mjsunit/es6/debug-promises/throw-caught-by-default-reject-handler.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 --allow-natives-syntax
 
 // Test debug events when we only listen to uncaught exceptions and
 // there is only a default reject handler for the to-be-rejected Promise.
-// We expect two Exception debug events:
-//  - when the first Promise is rejected and only has default reject handlers.
-//  - when the default reject handler passes the rejection on.
+// We expect only one debug event: when the first Promise is rejected
+// and only has default reject handlers. No event is triggered when
+// simply forwarding the rejection with .then's default handler.
 
 Debug = debug.Debug;
 
-var expected_events = 2;
+var expected_events = 1;
 var log = [];
 
 var resolve, reject;
 var p0 = new Promise(function(res, rej) { resolve = res; reject = rej; });
 var p1 = p0.then(function() {
   log.push("p0.then");
   throw new Error("123");  // event
 });
 var p2 = p1.then(function() {
   log.push("p1.then");
@@ skipping 10 matching lines @@
 })
 
 
 function listener(event, exec_state, event_data, data) {
   try {
     if (event == Debug.DebugEvent.Exception) {
       expected_events--;
       assertTrue(expected_events >= 0);
       assertTrue(event_data.uncaught());
       assertTrue(event_data.promise() instanceof Promise);
-      if (expected_events == 1) {
-        // p1 is rejected, uncaught except for its default reject handler.
-        assertTrue(
-            exec_state.frame(0).sourceLineText().indexOf("// event") > 0);
-        assertSame(p1, event_data.promise());
-      } else {
-        // p2 is rejected by p1's default reject handler.
-        assertEquals(0, exec_state.frameCount());
-        assertSame(p2, event_data.promise());
-      }
+      // p1 is rejected, uncaught except for its default reject handler.
+      assertTrue(
+          exec_state.frame(0).sourceLineText().indexOf("// event") > 0);
+      assertSame(p1, event_data.promise());
     }
   } catch (e) {
     %AbortJS(e + "\n" + e.stack);
   }
 }
 
 Debug.setBreakOnUncaughtException();
 Debug.setListener(listener);
 
 log.push("end main");
 
 function testDone(iteration) {
   function checkResult() {
     try {
       assertTrue(iteration < 10);
       if (expected_events === 0) {
         assertEquals(["resolve q", "end main", "resolve p", "p0.then"], log);
       } else {
         testDone(iteration + 1);
       }
     } catch (e) {
       %AbortJS(e + "\n" + e.stack);
     }
   }
 
   %EnqueueMicrotask(checkResult);
 }
 
 testDone(0);