Fix "unused variable" warnings.

chrome/browser/signin/signin_status_metrics_provider_chromeos_unittest.cc

 // Copyright 2014 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 "chrome/browser/signin/signin_status_metrics_provider_chromeos.h"
 
 #include <string>
 
 #include "base/files/file_path.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 TEST(SigninStatusMetricsProviderChromeOS, ComputeSigninStatusToUpload) {
-  SigninStatusMetricsProviderChromeOS metrics_provider =
-      SigninStatusMetricsProviderChromeOS();
+  SigninStatusMetricsProviderChromeOS metrics_provider;

[Peter Kasting, 2016/05/19 05:11:37]

This was an interesting case.  The old code requires the copy constructor to be
accessible from this location, even though it's not actually called. 
SigninStatusMetricsProviderChromeOS uses DISALLOW_COPY_AND_ASSIGN, but the old
definition for that only makes that constructor private; since this test is a
friend, it can see that private declaration.  And since the copy constructor
isn't actually accessed, it doesn't matter that it's never defined.

Switching to "= delete" means the old code here won't compile.  Luckily, the fix
is easy.

 
   SigninStatusMetricsProviderBase::SigninStatus status_to_upload =
       metrics_provider.ComputeSigninStatusToUpload(
           SigninStatusMetricsProviderBase::ALL_PROFILES_SIGNED_IN, true);
   EXPECT_EQ(SigninStatusMetricsProviderBase::ALL_PROFILES_SIGNED_IN,
             status_to_upload);
 
   status_to_upload = metrics_provider.ComputeSigninStatusToUpload(
       SigninStatusMetricsProviderBase::ALL_PROFILES_NOT_SIGNED_IN, false);
   EXPECT_EQ(SigninStatusMetricsProviderBase::ALL_PROFILES_NOT_SIGNED_IN,
             status_to_upload);
 
   status_to_upload = metrics_provider.ComputeSigninStatusToUpload(
       SigninStatusMetricsProviderBase::ALL_PROFILES_NOT_SIGNED_IN, true);
   EXPECT_EQ(SigninStatusMetricsProviderBase::MIXED_SIGNIN_STATUS,
             status_to_upload);
 
   status_to_upload = metrics_provider.ComputeSigninStatusToUpload(
       SigninStatusMetricsProviderBase::ALL_PROFILES_SIGNED_IN, false);
   EXPECT_EQ(SigninStatusMetricsProviderBase::ERROR_GETTING_SIGNIN_STATUS,
             status_to_upload);
 }