cache suggestions on change in priority sources

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

Index: pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart b/pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart
index 07b93f9a8231f3d3da76c122c0b7eae066a46394..c40763ca1ecb968f357952b5c27d0a25b3fd137f 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart
@@ -75,6 +75,15 @@ class DartCompletionManager extends CompletionManager {
         new DartCompletionCache(context, source));
   }
 
+  @override
+  void computeCache() {
+    waitForAnalysis().then((CompilationUnit unit) {
+      if (unit != null && !cache.isImportInfoCached(unit)) {
+        cache.computeImportInfo(unit, searchEngine);
+      }
+    });
+  }
+
   /**
    * Compute suggestions based upon cached information only
    * then send an initial response to the client.