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/1341510Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610010}

third_party/WebKit/LayoutTests/TestExpectations

@@ -2943,8 +2943,6 @@ crbug.com/626703 external/wpt/css/css-text/writing-system/writing-system-line-br
 crbug.com/626703 external/wpt/css/css-text/writing-system/writing-system-text-transform-001.html [ Failure ]
 crbug.com/626703 [ Win7 ] external/wpt/web-animations/animation-model/animation-types/accumulation-per-property.html [ Failure Timeout ]
 crbug.com/626703 [ Win7 ] external/wpt/IndexedDB/interleaved-cursors-large.html [ Crash ]
-crbug.com/626703 virtual/webrtc-wpt-unified-plan/external/wpt/webrtc/RTCPeerConnection-track-stats.https.html [ Timeout ]
-crbug.com/626703 external/wpt/webrtc/RTCPeerConnection-track-stats.https.html [ Timeout ]
 crbug.com/903383 external/wpt/css/filter-effects/filter-cb-abspos-inline-003.html [ Failure ]
 crbug.com/903383 external/wpt/css/filter-effects/css-filters-animation-combined-001.html [ Failure ]
 crbug.com/903383 external/wpt/css/filter-effects/css-filters-animation-blur.html [ Failure ]

third_party/WebKit/LayoutTests/external/wpt/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;
+    }
   }
 }