Remove MessageLoop destruction observer from mojo::Watcher.

mojo/public/cpp/system/tests/watcher_unittest.cc

Index: mojo/public/cpp/system/tests/watcher_unittest.cc
diff --git a/mojo/public/cpp/system/tests/watcher_unittest.cc b/mojo/public/cpp/system/tests/watcher_unittest.cc
index 5cb3ed23b7799571da5820a1d81492791b8267f1..ebeebf6777888a67aeeba7af1b6bf0290cd2d312 100644
--- a/mojo/public/cpp/system/tests/watcher_unittest.cc
+++ b/mojo/public/cpp/system/tests/watcher_unittest.cc
@@ -8,6 +8,7 @@
 
 #include "base/bind.h"
 #include "base/callback.h"
+#include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ -35,16 +36,10 @@ class WatcherTest : public testing::Test {
   WatcherTest() {}
   ~WatcherTest() override {}
 
-  void SetUp() override {
-    message_loop_.reset(new base::MessageLoop);
-  }
-
-  void TearDown() override {
-    message_loop_.reset();
-  }
+ private:
+  base::MessageLoop message_loop_;
 
- protected:
-  std::unique_ptr<base::MessageLoop> message_loop_;
+  DISALLOW_COPY_AND_ASSIGN(WatcherTest);
 };
 
 TEST_F(WatcherTest, WatchBasic) {
@@ -162,28 +157,6 @@ TEST_F(WatcherTest, CancelOnDestruction) {
   run_loop.Run();
 }
 
-TEST_F(WatcherTest, NotifyOnMessageLoopDestruction) {
-  ScopedMessagePipeHandle a, b;
-  CreateMessagePipe(nullptr, &a, &b);
-
-  bool notified = false;
-  Watcher b_watcher;
-  EXPECT_EQ(MOJO_RESULT_OK,
-            b_watcher.Start(b.get(), MOJO_HANDLE_SIGNAL_READABLE,
-                            OnReady([&] (MojoResult result) {
-                              EXPECT_EQ(MOJO_RESULT_ABORTED, result);
-                              notified = true;
-                            })));
-  EXPECT_TRUE(b_watcher.IsWatching());
-
-  message_loop_.reset();
-
-  EXPECT_TRUE(notified);
-
-  EXPECT_TRUE(b_watcher.IsWatching());
-  b_watcher.Cancel();
-}
-
 TEST_F(WatcherTest, CloseAndCancel) {
   ScopedMessagePipeHandle a, b;
   CreateMessagePipe(nullptr, &a, &b);