Validate the regex used in search.findTopLevelDeclarations.

pkg/analysis_server/lib/src/search/search_domain.dart

Index: pkg/analysis_server/lib/src/search/search_domain.dart
diff --git a/pkg/analysis_server/lib/src/search/search_domain.dart b/pkg/analysis_server/lib/src/search/search_domain.dart
index 4a0e1b7a4eed93d1bc69f3b069862cf01f2f5fa5..37c58a69e5811e06cf039dafa67807aa5422178c 100644
--- a/pkg/analysis_server/lib/src/search/search_domain.dart
+++ b/pkg/analysis_server/lib/src/search/search_domain.dart
@@ -118,6 +118,15 @@ class SearchDomainHandler implements protocol.RequestHandler {
   Future findTopLevelDeclarations(protocol.Request request) async {
     var params =
         new protocol.SearchFindTopLevelDeclarationsParams.fromRequest(request);
+    try {
+      // validate the regex
+      new RegExp(params.pattern);
+    } on FormatException catch (exception) {
+      server.sendResponse(new protocol.Response.invalidParameter(
+          request, 'pattern', exception.message));
+      return;
+    }
+
     await server.onAnalysisComplete;
     // respond
     String searchId = (_nextSearchId++).toString();