Rolling average work queue diagnostic (#24933).

pkg/analysis_server/test/integration/protocol_matchers.dart

Index: pkg/analysis_server/test/integration/protocol_matchers.dart
diff --git a/pkg/analysis_server/test/integration/protocol_matchers.dart b/pkg/analysis_server/test/integration/protocol_matchers.dart
index 6663f98f474931c7a65985d1d3f0e464c3365602..fed0c036d9ff6af410dd26b0e288d3d41289d4dc 100644
--- a/pkg/analysis_server/test/integration/protocol_matchers.dart
+++ b/pkg/analysis_server/test/integration/protocol_matchers.dart
@@ -1283,6 +1283,7 @@ final Matcher isCompletionSuggestionKind = new MatchesEnum("CompletionSuggestion
  *   "explicitFileCount": int
  *   "implicitFileCount": int
  *   "workItemQueueLength": int
+ *   "workItemQueueLengthAverage": String
  *   "cacheEntryExceptions": List<String>
  * }
  */
@@ -1292,6 +1293,7 @@ final Matcher isContextData = new LazyMatcher(() => new MatchesJsonObject(
     "explicitFileCount": isInt,
     "implicitFileCount": isInt,
     "workItemQueueLength": isInt,
+    "workItemQueueLengthAverage": isString,
     "cacheEntryExceptions": isListOf(isString)
   }));