Report promise reject with no handler (behind a flag).

src/promise.js

Index: src/promise.js
diff --git a/src/promise.js b/src/promise.js
index 37c10ec08eb298d5543738531168fe0315ca7854..ca9bc25f279ee45c48ce00f39af736de1b4d15c5 100644
--- a/src/promise.js
+++ b/src/promise.js
@@ -30,7 +30,7 @@ var promiseValue = GLOBAL_PRIVATE("Promise#value");
 var promiseOnResolve = GLOBAL_PRIVATE("Promise#onResolve");
 var promiseOnReject = GLOBAL_PRIVATE("Promise#onReject");
 var promiseRaw = GLOBAL_PRIVATE("Promise#raw");
-var promiseDebug = GLOBAL_PRIVATE("Promise#debug");
+var promiseHasReject = GLOBAL_PRIVATE("Promise#hasReject");
 var lastMicrotaskId = 0;
 
 (function() {
@@ -159,11 +159,8 @@ var lastMicrotaskId = 0;
 
   PromiseReject = function PromiseReject(promise, r) {
     // Check promise status to confirm that this reject has an effect.
-    // Check promiseDebug property to avoid duplicate event.
-    if (DEBUG_IS_ACTIVE &&
-        GET_PRIVATE(promise, promiseStatus) == 0 &&
-        !HAS_DEFINED_PRIVATE(promise, promiseDebug)) {
-      %DebugPromiseRejectEvent(promise, r);
+    if (GET_PRIVATE(promise, promiseStatus) == 0) {
+      %PromiseRejectEvent(promise, r);
     }
     PromiseDone(promise, -1, r, promiseOnReject)
   }
@@ -213,6 +210,10 @@ var lastMicrotaskId = 0;
                                                                // flatMap
     onResolve = IS_UNDEFINED(onResolve) ? PromiseIdResolveHandler : onResolve;
     onReject = IS_UNDEFINED(onReject) ? PromiseIdRejectHandler : onReject;
+    if (onReject != PromiseIdRejectHandler) {
+      // Mark this promise as having reject handler.
+      SET_PRIVATE(this, promiseHasReject, true);
+    }
     var deferred = %_CallFunction(this.constructor, PromiseDeferred);
     switch (GET_PRIVATE(this, promiseStatus)) {
       case UNDEFINED:
@@ -326,20 +327,18 @@ var lastMicrotaskId = 0;
   // Utility for debugger
 
   function PromiseHasRejectHandlerRecursive(promise) {
+    if (GET_PRIVATE(promise, promiseHasReject)) return true;
     var queue = GET_PRIVATE(promise, promiseOnReject);
     if (IS_UNDEFINED(queue)) return false;
-    // Do a depth first search for a reject handler that's not
-    // the default PromiseIdRejectHandler.
+    // Do a depth first search for a promise that has been marked as having
+    // a reject handler.
     for (var i = 0; i < queue.length; i += 2) {
-      if (queue[i] != PromiseIdRejectHandler) return true;
       if (PromiseHasRejectHandlerRecursive(queue[i + 1].promise)) return true;
     }
     return false;
   }
 
   PromiseHasRejectHandler = function PromiseHasRejectHandler() {
-    // Mark promise as already having triggered a reject event.
-    SET_PRIVATE(this, promiseDebug, true);
     return PromiseHasRejectHandlerRecursive(this);
   };