Test helper: In answer, apply remote description before local description.

This ensures that candidates generated at callee arrive after making
the caller ready to receive them.

Bug: chromium:1122106
Change-Id: Iae0643da57029db8df6b98ef417ee2d4136b2daa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2404346
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806165}

third_party/blink/web_tests/TestExpectations

@@ -6645,7 +6645,6 @@ crbug.com/1117613 media/video-error-networkState.html [ Failure Timeout ]
 crbug.com/1120330 virtual/threaded/external/wpt/feature-policy/experimental-features/vertical-scroll-disabled-scrollbar-tentative.html [ Pass Failure ]
 
 # Sheriff 2020-08-26
-crbug.com/1122106 external/wpt/webrtc/protocol/crypto-suite.https.html [ Pass Timeout ]
 crbug.com/1122742 http/tests/devtools/sources/debugger/source-frame-inline-breakpoint-decorations.js [ Pass Timeout ]
 
 crbug.com/1122582 external/wpt/html/cross-origin-opener-policy/coop-csp-sandbox-navigate.https.html [ Pass Failure ]

third_party/blink/web_tests/external/wpt/webrtc/RTCPeerConnection-helper.js

@@ -539,8 +539,12 @@ async function exchangeOffer(caller, callee) {
 }
 // Performs an answer exchange caller -> callee.
 async function exchangeAnswer(caller, callee) {
-  await callee.setLocalDescription(await callee.createAnswer());
-  await caller.setRemoteDescription(callee.localDescription);
+  // Note that caller's remote description must be set first; if not,
+  // there's a chance that candidates from callee arrive at caller before
+  // it has a remote description to apply them to.
+  const answer = await callee.createAnswer();
+  await caller.setRemoteDescription(answer);
+  await callee.setLocalDescription(answer);
 }
 async function exchangeOfferAnswer(caller, callee) {
   await exchangeOffer(caller, callee);