Experimental `getDiagnostics` request (#24480).

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 3bd16da6d047b06bf27647c815b66589cfa2f297..3f0da6c7652afc8d5bd2ef1c565bd310cb966308 100644
--- a/pkg/analysis_server/test/integration/protocol_matchers.dart
+++ b/pkg/analysis_server/test/integration/protocol_matchers.dart
@@ -1007,6 +1007,23 @@ final Matcher isExecutionLaunchDataParams = new LazyMatcher(() => new MatchesJso
   }));
 
 /**
+ * experimental.getDiagnostics params
+ */
+final Matcher isExperimentalGetDiagnosticsParams = isNull;
+
+/**
+ * experimental.getDiagnostics result
+ *
+ * {
+ *   "contexts": List<ContextInfo>
+ * }
+ */
+final Matcher isExperimentalGetDiagnosticsResult = new LazyMatcher(() => new MatchesJsonObject(
+  "experimental.getDiagnostics result", {
+    "contexts": isListOf(isContextInfo)
+  }));
+
+/**
  * AddContentOverlay
  *
  * {
@@ -1259,6 +1276,26 @@ final Matcher isCompletionSuggestionKind = new MatchesEnum("CompletionSuggestion
 ]);
 
 /**
+ * ContextInfo
+ *
+ * {
+ *   "name": String
+ *   "explicitlyAnalyzedFiles": int
+ *   "implicitlyAnalyzedFiles": int
+ *   "workItemQueueLength": int
+ *   "cacheEntryExceptions": List<String>
+ * }
+ */
+final Matcher isContextInfo = new LazyMatcher(() => new MatchesJsonObject(
+  "ContextInfo", {
+    "name": isString,
+    "explicitlyAnalyzedFiles": isInt,
+    "implicitlyAnalyzedFiles": isInt,
+    "workItemQueueLength": isInt,
+    "cacheEntryExceptions": isListOf(isString)
+  }));
+
+/**
  * Element
  *
  * {