include unimported sdk lib types as low priority suggestions

pkg/analysis_server/lib/src/services/completion/dart_completion_cache.dart

Index: pkg/analysis_server/lib/src/services/completion/dart_completion_cache.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart_completion_cache.dart b/pkg/analysis_server/lib/src/services/completion/dart_completion_cache.dart
index 9cc5f663d05dbc5a8e0636aa3ea9ac2eb5e78327..17127f7eb9e6e5cc720fd146a7b1b51f3e2f3d31 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart_completion_cache.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart_completion_cache.dart
@@ -277,10 +277,11 @@ class DartCompletionCache extends CompletionCache {
    */
   void _addNonImportedElementSuggestions(
       List<SearchMatch> matches, Set<LibraryElement> excludedLibs) {
+    AnalysisContext sdkContext = context.sourceFactory.dartSdk.context;
     matches.forEach((SearchMatch match) {
       if (match.kind == MatchKind.DECLARATION) {
         Element element = match.element;
-        if (element.context == context &&
+        if ((element.context == context || element.context == sdkContext) &&
             element.isPublic &&
             !excludedLibs.contains(element.library) &&
             !_importedCompletions.contains(element.displayName)) {