Add NullByteStore, that does not store any data.

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

Index: pkg/analyzer/test/src/dart/analysis/byte_store_test.dart
diff --git a/pkg/analyzer/test/src/dart/analysis/byte_store_test.dart b/pkg/analyzer/test/src/dart/analysis/byte_store_test.dart
index 9da3f0b6a9ebba19c30f059bd1b0e5b36cf29115..484a99fe10773105554a8e7af32d4fd1e217d661 100644
--- a/pkg/analyzer/test/src/dart/analysis/byte_store_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/byte_store_test.dart
@@ -10,9 +10,14 @@ import 'package:typed_mock/typed_mock.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(MemoryCachingByteStoreTest);
+    defineReflectiveTests(NullByteStoreTest);
   });
 }
 
+List<int> _b(int length) {

[Brian Wilkerson, 2017/01/26 14:51:18]

This is only used in one place. Please consider inlining it, or at the very
least use a name that has some semantic value.

+  return new List<int>(length);
+}
+
 @reflectiveTest
 class MemoryCachingByteStoreTest {
   test_get_notFound_evict() {
@@ -99,9 +104,17 @@ class MemoryCachingByteStoreTest {
     expect(cachingStore.get('2'), isNull);
     expect(cachingStore.get('3'), hasLength(30));
   }
+}
+
+@reflectiveTest
+class NullByteStoreTest {
+  test_get() {
+    var store = new NullByteStore();
+
+    expect(store.get('1'), isNull);
 
-  static List<int> _b(int length) {
-    return new List<int>(length);
+    store.put('1', _b(10));
+    expect(store.get('1'), isNull);
   }
 }