Don't sent errors for general files if the file has the same signature.

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

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.driver;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 2195 matching lines @@
     expect(allResults, hasLength(1));
     AnalysisResult result = allResults.single;
     expect(result.path, testFile);
     expect(result.uri.toString(), 'package:test/test.dart');
     expect(result.content, isNull);
     expect(result.contentHash, _md5(content));
     expect(result.unit, isNull);
     expect(result.errors, hasLength(0));
   }
 
+  test_results_skipNotAffected() async {
+    var a = _p('/test/lib/a.dart');
+    var b = _p('/test/lib/b.dart');
+    provider.newFile(a, 'class A {}');
+    provider.newFile(b, 'class B {}');
+
+    driver.addFile(a);
+    driver.addFile(b);
+    await scheduler.waitForIdle();
+
+    expect(allResults, hasLength(2));
+    allResults.clear();
+
+    // Update a.dart and notify.
+    provider.updateFile(a, 'class A2 {}');
+    driver.changeFile(a);
+
+    // Only result for a.dart should be produced, b.dart is not affected.
+    await scheduler.waitForIdle();
+    expect(allResults, hasLength(1));
+  }
+
   test_results_status() async {
     addTestFile('int f() => 42;');
     await scheduler.waitForIdle();
 
     expect(allStatuses, hasLength(2));
     expect(allStatuses[0].isAnalyzing, isTrue);
     expect(allStatuses[0].isIdle, isFalse);
     expect(allStatuses[1].isAnalyzing, isFalse);
     expect(allStatuses[1].isIdle, isTrue);
   }
@@ skipping 130 matching lines @@
    * Return the [provider] specific path for the given Posix [path].
    */
   String _p(String path) => provider.convertPath(path);
 
   static String _md5(String content) {
     return hex.encode(md5.convert(UTF8.encode(content)).bytes);
   }
 }
 
 class _SourceMock extends TypedMock implements Source {}