Idea exploring a solution to the Performance Problem @bmeurer brought…

… up: https://twitter.com/bmeurer/status/960440074574934016

spec.html

@@ -37304,7 +37304,6 @@ <h1>RejectPromise ( _promise_, _reason_ )</h1>
           1. Set _promise_.[[PromiseFulfillReactions]] to *undefined*.
           1. Set _promise_.[[PromiseRejectReactions]] to *undefined*.
           1. Set _promise_.[[PromiseState]] to `"rejected"`.
-          1. If _promise_.[[PromiseIsHandled]] is *false*, perform HostPromiseRejectionTracker(_promise_, `"reject"`).
           1. Return TriggerPromiseReactions(_reactions_, _reason_).
         </emu-alg>
       </emu-clause>
@@ -37361,6 +37360,7 @@ <h1>PromiseReactionJob ( _reaction_, _argument_ )</h1>
             1. If _type_ is `"Fulfill"`, let _handlerResult_ be NormalCompletion(_argument_).
             1. Else,
               1. Assert: _type_ is `"Reject"`.
+              1. If _promise_.[[PromiseIsHandled]] is *false*, perform HostPromiseRejectionTracker(_promise_, `"reject"`).
               1. Let _handlerResult_ be Completion {[[Type]]: ~throw~, [[Value]]: _argument_, [[Target]]: ~empty~}.
           1. Else, let _handlerResult_ be Call(_handler_, *undefined*, &laquo; _argument_ &raquo;).
           1. If _handlerResult_ is an abrupt completion, then
@@ -37734,7 +37734,6 @@ <h1>PerformPromiseThen ( _promise_, _onFulfilled_, _onRejected_, _resultCapabili
             1. Else,
               1. Assert: The value of _promise_.[[PromiseState]] is `"rejected"`.
               1. Let _reason_ be _promise_.[[PromiseResult]].
-              1. If _promise_.[[PromiseIsHandled]] is *false*, perform HostPromiseRejectionTracker(_promise_, `"handle"`).
               1. Perform EnqueueJob(`"PromiseJobs"`, PromiseReactionJob, &laquo; _rejectReaction_, _reason_ &raquo;).
             1. Set _promise_.[[PromiseIsHandled]] to *true*.
             1. Return _resultCapability_.[[Promise]].