Do nothing if [changeFile] reported, but the file content is the same.

pkg/analyzer/test/src/dart/analysis/driver_test.dart

Index: pkg/analyzer/test/src/dart/analysis/driver_test.dart
diff --git a/pkg/analyzer/test/src/dart/analysis/driver_test.dart b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
index 34e20efdbb12f04d3580a5b54762526a16ef8807..fb37be9a44669fdb74c9a4c84c6c38f1c7220ac0 100644
--- a/pkg/analyzer/test/src/dart/analysis/driver_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
@@ -77,7 +77,7 @@ class DriverTest {
           })
         ], null, provider),
         new AnalysisOptionsImpl()..strongMode = true);
-    driver.status.lastWhere((status) {
+    driver.status.listen((status) {
       allStatuses.add(status);
       if (status.isIdle) {
         idleStatusMonitor.notify();
@@ -141,6 +141,30 @@ var A = B;
     }
   }
 
+  test_changeFile_noContentChange_noNewResult() async {
+    _addTestFile('main() {}', priority: true);
+
+    // Initial analysis.
+    await _waitForIdle();
+    expect(allResults, hasLength(1));
+
+    // Update the file, but don't notify the driver.
+    // Don't update the file in the file system.
+    // But tell the driver the the file was changed.
+    // The driver should eventually check the file and ignore.
+    allStatuses.clear();
+    allResults.clear();
+    driver.changeFile(testFile);
+
+    // The driver switched to analysis and back to idle.
+    await _waitForIdle();
+    expect(allStatuses, hasLength(2));
+    expect(allStatuses.map((status) => status.isAnalyzing), [true, false]);
+
+    // No new results.
+    expect(allResults, isEmpty);
+  }
+
   test_changeFile_selfConsistent() async {
     var a = _p('/test/lib/a.dart');
     var b = _p('/test/lib/b.dart');