Discard pending notifications on the same source change.

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

Index: pkg/analysis_server/lib/src/operation/operation.dart
diff --git a/pkg/analysis_server/lib/src/operation/operation.dart b/pkg/analysis_server/lib/src/operation/operation.dart
index 03fd9135d63016097f47bc45105e120ceb5ea53d..e9ed101115ef5be2dd7f08e6513fa923a4fe5497 100644
--- a/pkg/analysis_server/lib/src/operation/operation.dart
+++ b/pkg/analysis_server/lib/src/operation/operation.dart
@@ -5,6 +5,7 @@
 library operation;
 
 import 'package:analysis_server/src/analysis_server.dart';
+import 'package:analyzer/src/generated/source.dart';
 
 
 /**
@@ -58,3 +59,16 @@ class ServerOperationPriority {
   @override
   String toString() => name;
 }
+
+
+/**
+ * [SourceSensitiveOperation] can decide if the operation should be discarded
+ * before a change is applied to a [Source].
+ */
+abstract class SourceSensitiveOperation extends ServerOperation {
+  /**
+   * The given [source] is about to be changed.
+   * Check if this [SourceSensitiveOperation] should be discarded.
+   */
+  bool shouldBeDiscardedOnSourceChange(Source source);
+}