[ObjC ARC] Converts ios/chrome/app/application_delegate:unit_tests to ARC.

ios/chrome/app/application_delegate/memory_warning_helper_unittest.mm

 // Copyright 2016 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.
 
 #import "ios/chrome/app/application_delegate/memory_warning_helper.h"
 
 #include "base/mac/bind_objc_block.h"
-#import "base/mac/scoped_nsobject.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/threading/thread.h"
 #import "ios/chrome/browser/metrics/previous_session_info.h"
 #include "testing/platform_test.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 using previous_session_info_constants::
     kDidSeeMemoryWarningShortlyBeforeTerminating;
 
 class MemoryWarningHelperTest : public PlatformTest {
  protected:
   MemoryWarningHelperTest() {
     // Set up |memory_pressure_listener_| to invoke |OnMemoryPressure| which
     // will store the memory pressure level sent to the callback in
     // |memory_pressure_level_| so that tests can verify the level is correct.
     memory_pressure_listener_.reset(new base::MemoryPressureListener(base::Bind(
         &MemoryWarningHelperTest::OnMemoryPressure, base::Unretained(this))));
     memory_pressure_level_ =
         base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE;
   }
 
   base::MemoryPressureListener::MemoryPressureLevel GetMemoryPressureLevel() {
     return memory_pressure_level_;
   }
 
   MemoryWarningHelper* GetMemoryHelper() {
     if (!memory_helper_) {
-      memory_helper_.reset([[MemoryWarningHelper alloc] init]);
+      memory_helper_ = [[MemoryWarningHelper alloc] init];
     }
     return memory_helper_;
   }
 
   // Callback for |memory_pressure_listener_|.
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level) {
     memory_pressure_level_ = memory_pressure_level;
     run_loop_.QuitWhenIdle();
   }
 
   void RunMessageLoop() { run_loop_.Run(); }
 
  private:
   base::MessageLoop message_loop_;
   base::RunLoop run_loop_;
   base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level_;
   std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_;
-  base::scoped_nsobject<MemoryWarningHelper> memory_helper_;
+  MemoryWarningHelper* memory_helper_;
 
   DISALLOW_COPY_AND_ASSIGN(MemoryWarningHelperTest);
 };
 
 // Invokes resetForegroundMemoryWarningCount and verifies the
 // foregroundMemoryWarningCount is setted to 0.
 TEST_F(MemoryWarningHelperTest, VerifyForegroundMemoryWarningCountReset) {
   // Setup.
   [GetMemoryHelper() handleMemoryPressure];
   ASSERT_TRUE(GetMemoryHelper().foregroundMemoryWarningCount != 0);
@@ skipping 29 matching lines @@
   // Action.
   [GetMemoryHelper() handleMemoryPressure];
 
   // Tests.
   EXPECT_TRUE([[NSUserDefaults standardUserDefaults]
       boolForKey:kDidSeeMemoryWarningShortlyBeforeTerminating]);
   EXPECT_FALSE(memoryWarningFlagBeforeAlert);
   EXPECT_EQ(foregroundMemoryWarningCountBeforeWarning + 1,
             GetMemoryHelper().foregroundMemoryWarningCount);
 }