Make sure sideload wipeout doesn't interfere with the tests.

chrome/browser/extensions/extension_browsertest.h

 // 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_EXTENSION_BROWSERTEST_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_BROWSERTEST_H_
 
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 236 matching lines @@
   // When waiting for visible page action count to change, we wait until it
   // reaches this value.
   int target_visible_page_action_count_;
 
   // Make the current channel "dev" for the duration of the test.
   extensions::Feature::ScopedCurrentChannel current_channel_;
 
   // Disable external install UI.
   extensions::FeatureSwitch::ScopedOverride
       override_prompt_for_external_extensions_;
+
+  // Disable the sideload wipeout UI.
+  extensions::FeatureSwitch::ScopedOverride
+      override_sideload_wipeout_;
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_BROWSERTEST_H_