Mark webrtc/idlharness.https.window.js as timeout=long

On Chromium CI, this occasionally dips above 6s and times out. Looks
like its just a bit slow, not hanging entirely, so giving it more time
to finish seems ok.

Bug: 1033652
Change-Id: I1ea1ee51b19500aa99bbb318a8124abfce7abef3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2115517
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755893}

third_party/blink/web_tests/TestExpectations

@@ -6174,7 +6174,7 @@ crbug.com/1006759 inspector-protocol/heap-profiler/heap-snapshot-with-multiple-r
 crbug.com/1006759 inspector-protocol/heap-profiler/heap-snapshot-with-no-detached-iframe.js [ Pass Failure ]
 
 # Sheriff 2019-12-13
-crbug.com/1032451 virtual/webrtc-wpt-plan-b/external/wpt/webrtc/idlharness.https.window.html [ Failure Timeout Pass ]
+crbug.com/1032451 [ Win7 ] virtual/webrtc-wpt-plan-b/external/wpt/webrtc/idlharness.https.window.html [ Failure Pass ]
 crbug.com/1033852 [ Win7 ] virtual/omt-worker-fetch/external/wpt/fetch/api/idlharness.any.sharedworker.html [ Failure ]
 crbug.com/1033387 [ Mac ] http/tests/portals/crbug-1031677.html [ Pass Timeout Crash ]
 

third_party/blink/web_tests/external/wpt/webrtc/idlharness.https.window.js

 // META: script=/resources/WebIDLParser.js
 // META: script=/resources/idlharness.js
 // META: script=./RTCPeerConnection-helper.js
+// META: timeout=long
 
 'use strict';