Prevent timeout when remote stats are not implemented

This prevents a failure in RTCP messsaging from masking
other failures. It's up to other tests to actually
verify that RTCP stats have been delivered.

Bug: 904574
Change-Id: Ie641d5275372b4c10ad5fa3a39ae38c36f974482
Reviewed-on: https://chromium-review.googlesource.com/c/1341510
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610010}

webrtc/RTCPeerConnection-helper.js

@@ -251,6 +251,8 @@ function createDataChannelPair(
 
 // Wait for RTP and RTCP stats to arrive
 async function waitForRtpAndRtcpStats(pc) {
+  // If remote stats are never reported, return after 5 seconds.
+  const startTime = performance.now();
   while (true) {
     const report = await pc.getStats();
     const stats = [...report.values()].filter(({type}) => type.endsWith("bound-rtp"));
@@ -259,6 +261,9 @@ async function waitForRtpAndRtcpStats(pc) {
     if (stats.length && stats.every(({localId, remoteId}) => localId || remoteId)) {
       break;
     }
+    if (performance.now() > startTime + 5000) {
+      break;
+    }
   }
 }