Implement 'Import Library' Quick Fix for the new analysis driver.

pkg/analysis_server/lib/src/analysis_server.dart

Index: pkg/analysis_server/lib/src/analysis_server.dart
diff --git a/pkg/analysis_server/lib/src/analysis_server.dart b/pkg/analysis_server/lib/src/analysis_server.dart
index cff64d0dcf1a201cb84be2a40652f9cd2631ec28..8f2290716f4bb09c36586f77479cff8005876766 100644
--- a/pkg/analysis_server/lib/src/analysis_server.dart
+++ b/pkg/analysis_server/lib/src/analysis_server.dart
@@ -1964,6 +1964,11 @@ class ServerContextManagerCallbacks extends ContextManagerCallbacks {
       sendAnalysisNotificationFlushResults(analysisServer, flushedFiles);
       nd.AnalysisDriver driver = analysisServer.driverMap.remove(folder);
       driver.dispose();
+      // Remove cached priority results for the driver.
+      var results = analysisServer.priorityFileResults;
+      results.keys
+          .where((key) => results[key].driver == driver)
+          .forEach(results.remove);
     } else {
       AnalysisContext context = analysisServer.folderMap.remove(folder);
       sendAnalysisNotificationFlushResults(analysisServer, flushedFiles);