LabelObserver is no longer retained by the label

ios/chrome/browser/ui/util/label_observer_unittest.mm

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ios/chrome/browser/ui/util/label_observer.h"
 
 #import "base/mac/scoped_nsobject.h"
 #include "base/time/time.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/gtest_mac.h"
 #include "testing/platform_test.h"
 #include "url/gurl.h"
 
 namespace {
 
 class LabelObserverTest : public PlatformTest {
  protected:
   void SetUp() override {
     label_.reset([[UILabel alloc] initWithFrame:CGRectZero]);
+    observer_.reset([[LabelObserver observerForLabel:label_.get()] retain]);
+    [observer_ startObserving];
   }
 
+  ~LabelObserverTest() override { [observer_ stopObserving]; }
+
   UILabel* label() { return label_.get(); }
-  LabelObserver* observer() { return [LabelObserver observerForLabel:label()]; }
+  LabelObserver* observer() { return observer_.get(); }
 
   base::scoped_nsobject<UILabel> label_;
+  base::scoped_nsobject<LabelObserver> observer_;
 };
 
 // Tests that all types of LabelObserverActions are successfully called.
 TEST_F(LabelObserverTest, SimpleTest) {
   __block BOOL text_action_called = NO;
   [observer() addTextChangedAction:^(UILabel* label) {
     text_action_called = YES;
   }];
   label().text = @"text";
   EXPECT_TRUE(text_action_called);
@@ skipping 38 matching lines @@
     EXPECT_TRUE(first_action_called);
     EXPECT_FALSE(second_action_called);
     second_action_called = YES;
   }];
   label().text = @"test";
   EXPECT_TRUE(first_action_called);
   EXPECT_TRUE(second_action_called);
 }
 
 }  // namespace