RTCIceCandidateStats.deleted = false added.

Since previously, only the deleted = false case is supported, but now
that stat is added. It's a recent addition to the spec:
https://w3c.github.io/webrtc-stats/#dom-rtcicecandidatestats-deleted

BUG=webrtc:6756, chromium:632723, chromium:627816

Review-Url: https://codereview.webrtc.org/2591963003
Cr-Commit-Position: refs/heads/master@{#15871}
diff --git a/webrtc/api/rtcstats_integrationtest.cc b/webrtc/api/rtcstats_integrationtest.cc
index 556907c..53c73f3 100644
--- a/webrtc/api/rtcstats_integrationtest.cc
+++ b/webrtc/api/rtcstats_integrationtest.cc
@@ -397,6 +397,7 @@
     verifier.TestMemberIsDefined(candidate.candidate_type);
     verifier.TestMemberIsNonNegative<int32_t>(candidate.priority);
     verifier.TestMemberIsUndefined(candidate.url);
+    verifier.TestMemberIsDefined(candidate.deleted);
     return verifier.ExpectAllMembersSuccessfullyTested();
   }