Add AnalysisContext.onResultInvalidated(descriptor).

pkg/analyzer/test/src/context/context_test.dart

Index: pkg/analyzer/test/src/context/context_test.dart
diff --git a/pkg/analyzer/test/src/context/context_test.dart b/pkg/analyzer/test/src/context/context_test.dart
index d7e0a589a8332abb27ec4495d480e703e2f97f9f..cf4db30c93642040281eeee8fbe4f669fd8137df 100644
--- a/pkg/analyzer/test/src/context/context_test.dart
+++ b/pkg/analyzer/test/src/context/context_test.dart
@@ -1463,6 +1463,44 @@ main() {}''');
     expect(context.isServerLibrary(source), isFalse);
   }
 
+  void test_onResultInvalidated_removeSource() {
+    Source source = addSource('/test.dart', 'main() {}');
+    bool listenerInvoked = false;
+    context
+        .onResultInvalidated(RESOLVED_UNIT)
+        .listen((InvalidatedResult event) {
+      Source eventSource = event.entry.target.source;
+      expect(event.descriptor, RESOLVED_UNIT);
+      expect(eventSource, source);
+      listenerInvoked = true;
+    });
+    _analyzeAll_assertFinished();
+    // apply changes
+    expect(listenerInvoked, false);
+    context.applyChanges(new ChangeSet()..removedSource(source));
+    // verify
+    expect(listenerInvoked, isTrue);
+  }
+
+  void test_onResultInvalidated_setContents() {
+    Source source = addSource('/test.dart', 'main() {}');
+    bool listenerInvoked = false;
+    context
+        .onResultInvalidated(RESOLVED_UNIT)
+        .listen((InvalidatedResult event) {
+      Source eventSource = event.entry.target.source;
+      expect(event.descriptor, RESOLVED_UNIT);
+      expect(eventSource, source);
+      listenerInvoked = true;
+    });
+    _analyzeAll_assertFinished();
+    // apply changes
+    expect(listenerInvoked, false);
+    context.setContents(source, 'class B {}');
+    // verify
+    expect(listenerInvoked, isTrue);
+  }
+
   void test_parseCompilationUnit_errors() {
     Source source = addSource("/lib.dart", "library {");
     CompilationUnit compilationUnit = context.parseCompilationUnit(source);