Cherry-pick r44373, r44378, and r44275.

pkg/analysis_server/lib/src/operation/operation_queue.dart

Index: pkg/analysis_server/lib/src/operation/operation_queue.dart
diff --git a/pkg/analysis_server/lib/src/operation/operation_queue.dart b/pkg/analysis_server/lib/src/operation/operation_queue.dart
index 7ea825759599e6e047531dc6ef25c9c6a66f3a3c..ced4a8c9e54f74c59d2c92e382f5b5fc6558d6b0 100644
--- a/pkg/analysis_server/lib/src/operation/operation_queue.dart
+++ b/pkg/analysis_server/lib/src/operation/operation_queue.dart
@@ -8,6 +8,7 @@ import 'dart:collection';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/operation/operation.dart';
+import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 
 /**
@@ -51,6 +52,16 @@ class ServerOperationQueue {
   }
 
   /**
+   * The given [context] has been removed, so all pending operations that refer
+   * to it should be removed from the queue.
+   */
+  void contextRemoved(AnalysisContext context) {
+    for (Queue<ServerOperation> queue in _queues) {
+      queue.removeWhere((operation) => operation.context == context);
+    }
+  }
+
+  /**
    * Return the next operation to perform, or `null` if the queue is empty.
    * This method does not change the queue.
    */