Change which ExceptionEvents are triggered by Promises

src/js/harmony-async-await.js

Index: src/js/harmony-async-await.js
diff --git a/src/js/harmony-async-await.js b/src/js/harmony-async-await.js
index 3a48d0c1005842a97bb9c868ae1240aef4a3bd95..192e041e554fbf8d4a1811848ffa801a94cc695f 100644
--- a/src/js/harmony-async-await.js
+++ b/src/js/harmony-async-await.js
@@ -41,7 +41,8 @@ function AsyncFunctionAwait(generator, value) {
   var onRejected =
       (sentError) => %_Call(AsyncFunctionThrow, generator, sentError);
 
-  var throwawayCapability = NewPromiseCapability(GlobalPromise);
+  // false debugEvent to avoid redundant ExceptionEvents
+  var throwawayCapability = NewPromiseCapability(GlobalPromise, false);
   return PerformPromiseThen(promise, onFulfilled, onRejected,
                             throwawayCapability);
 }