Support for searching LabelElements in SearchEngine.

pkg/analysis_server/lib/src/services/search/search_engine_internal.dart

Index: pkg/analysis_server/lib/src/services/search/search_engine_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/search/search_engine_internal.dart b/pkg/analysis_server/lib/src/services/search/search_engine_internal.dart
index bc49db0da66f11ce4ffc718e645ffc66a5cf3c2f..712d8a4f36758cd6cd2d61f1d3d7bfedbf58a300 100644
--- a/pkg/analysis_server/lib/src/services/search/search_engine_internal.dart
+++ b/pkg/analysis_server/lib/src/services/search/search_engine_internal.dart
@@ -81,6 +81,8 @@ class SearchEngineImpl implements SearchEngine {
           element as PropertyAccessorElement);
     } else if (element.kind == ElementKind.IMPORT) {
       return _searchReferences_Import(element as ImportElement);
+    } else if (element.kind == ElementKind.LABEL) {
+      return _searchReferences_Label(element as LabelElement);
     } else if (element.kind == ElementKind.LIBRARY) {
       return _searchReferences_Library(element as LibraryElement);
     } else if (element.kind == ElementKind.LOCAL_VARIABLE) {
@@ -142,7 +144,6 @@ class SearchEngineImpl implements SearchEngine {
 
   Future<List<SearchMatch>>
       _searchReferences_CompilationUnit(CompilationUnitElement unit) {
-    // TODO(merge?)
     _Requestor requestor = new _Requestor(_index);
     requestor.add(unit, IndexConstants.IS_REFERENCED_BY, MatchKind.REFERENCE);
     return requestor.merge();
@@ -206,6 +207,15 @@ class SearchEngineImpl implements SearchEngine {
     return requestor.merge();
   }
 
+  Future<List<SearchMatch>> _searchReferences_Label(LabelElement variable) {
+    _Requestor requestor = new _Requestor(_index);
+    requestor.add(
+        variable,
+        IndexConstants.IS_REFERENCED_BY,
+        MatchKind.REFERENCE);
+    return requestor.merge();
+  }
+
   Future<List<SearchMatch>> _searchReferences_Library(LibraryElement library) {
     _Requestor requestor = new _Requestor(_index);
     requestor.add(