[ObjC ARC] Converts ios/chrome/test/earl_grey:test_support to ARC.

ios/chrome/test/earl_grey/chrome_assertions.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/test/earl_grey/chrome_assertions.h"
 
 #import <EarlGrey/EarlGrey.h>
 
 #include "base/format_macros.h"
 #import "ios/chrome/test/app/tab_test_util.h"
 #import "ios/testing/wait_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace chrome_test_util {
 
 void AssertMainTabCount(NSUInteger expected_tab_count) {
   // Allow the UI to become idle, in case any tabs are being opened or closed.
   [[GREYUIThreadExecutor sharedInstance] drainUntilIdle];
   GREYAssert(testing::WaitUntilConditionOrTimeout(
                  testing::kWaitForUIElementTimeout,
                  ^{
                    return GetMainTabCount() == expected_tab_count;
                  }),
              @"Did not receive %" PRIuNS " tabs", expected_tab_count);
 }
 
 void AssertIncognitoTabCount(NSUInteger expected_tab_count) {
   // Allow the UI to become idle, in case any tabs are being opened or closed.
   [[GREYUIThreadExecutor sharedInstance] drainUntilIdle];
   ConditionBlock condition = ^{
     return GetIncognitoTabCount() == expected_tab_count;
   };
   GREYAssert(testing::WaitUntilConditionOrTimeout(
                  testing::kWaitForUIElementTimeout, condition),
              @"Did not receive %" PRIuNS " incognito tabs", expected_tab_count);
 }
 
 }  // namespace chrome_test_util