Avoid changing enabled features while the browser is already running.

content/public/test/browser_test_base.cc

 // Copyright (c) 2011 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 "content/public/test/browser_test_base.h"
 
 #include <stddef.h>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 232 matching lines @@
   if (!enabled_features.empty())
     command_line->AppendSwitchASCII(switches::kEnableFeatures,
                                     enabled_features);
   if (!disabled_features.empty())
     command_line->AppendSwitchASCII(switches::kDisableFeatures,
                                     disabled_features);
 
   // Need to wipe feature list clean, since BrowserMain calls
   // FeatureList::SetInstance, which expects no instance to exist.
   base::FeatureList::ClearInstanceForTesting();
+  base::FeatureList::BlockOverridingInstanceForTesting(true);
 
   base::Closure* ui_task =
       new base::Closure(
           base::Bind(&BrowserTestBase::ProxyRunTestOnMainThreadLoop,
                      base::Unretained(this)));
 
 #if defined(OS_ANDROID)
   MainFunctionParams params(*command_line);
   params.ui_task = ui_task;
   // TODO(phajdan.jr): Check return code, http://crbug.com/374738 .
   BrowserMain(params);
 #else
   GetContentMainParams()->ui_task = ui_task;
   EXPECT_EQ(expected_exit_code_, ContentMain(*GetContentMainParams()));
 #endif
   TearDownInProcessBrowserTestFixture();
+  base::FeatureList::BlockOverridingInstanceForTesting(false);
 }
 
 void BrowserTestBase::TearDown() {
 }
 
 void BrowserTestBase::ProxyRunTestOnMainThreadLoop() {
 #if defined(OS_POSIX)
   g_browser_process_pid = base::GetCurrentProcId();
   signal(SIGSEGV, DumpStackTraceSignalHandler);
 
@@ skipping 129 matching lines @@
   if (mojo_rules.empty())
     return;
 
   mojom::NetworkServiceTestPtr network_service_test;
   ServiceManagerConnection::GetForProcess()->GetConnector()->BindInterface(
       mojom::kNetworkServiceName, &network_service_test);
   network_service_test->AddRules(std::move(mojo_rules));
 }
 
 }  // namespace content