Use ENABLE_PRE_SYNC_BACKUP to disable test on iOS.

chrome/browser/sync/profile_sync_service_unittest.cc

 // Copyright (c) 2012 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 "base/basictypes.h"
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/run_loop.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 400 matching lines @@
   ExpectSyncBackendHostCreation(1);
 
   service()->UnsuppressAndStart();
   EXPECT_TRUE(service()->sync_initialized());
   EXPECT_FALSE(profile()->GetPrefs()->GetBoolean(
       sync_driver::prefs::kSyncSuppressStart));
 }
 
 // Certain ProfileSyncService tests don't apply to Chrome OS, for example
 // things that deal with concepts like "signing out" and policy.
-#if defined(OS_WIN) || defined(OS_MACOSX) || (defined(OS_LINUX) && !defined(OS_CHROMEOS))
+#if defined(ENABLE_PRE_SYNC_BACKUP)
 TEST_F(ProfileSyncServiceTest, EnableSyncAndSignOutDesktop) {
   CreateService(browser_sync::AUTO_START);
   ExpectDataTypeManagerCreation(2);
   ExpectSyncBackendHostCreation(2);
   IssueTestTokens();
   Initialize();
 
   EXPECT_TRUE(service()->sync_initialized());
   EXPECT_FALSE(profile()->GetPrefs()->GetBoolean(
       sync_driver::prefs::kSyncSuppressStart));
@@ skipping 161 matching lines @@
   // See that we can override the URL with a flag.
   CommandLine command_line(
       base::FilePath(base::FilePath(FILE_PATH_LITERAL("chrome.exe"))));
   command_line.AppendSwitchASCII(switches::kSyncServiceURL, "https://foo/bar");
   EXPECT_EQ("https://foo/bar",
             ProfileSyncService::GetSyncServiceURL(command_line).spec());
 }
 
 }  // namespace
 }  // namespace browser_sync