Create --disable-extensions-except switch

chrome/browser/extensions/extension_system_impl.h

 // 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_EXTENSION_SYSTEM_IMPL_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_SYSTEM_IMPL_H_
 
 #include <string>
 
+#include "base/command_line.h"
 #include "base/macros.h"
 #include "build/build_config.h"
 #include "extensions/browser/extension_system.h"
 #include "extensions/common/one_shot_event.h"
 
 class Profile;
 class ValueStore;
 
 namespace extensions {
 
@@ skipping 111 matching lines @@
 
     std::unique_ptr<UninstallPingSender> uninstall_ping_sender_;
 
 #if defined(OS_CHROMEOS)
     std::unique_ptr<chromeos::DeviceLocalAccountManagementPolicyProvider>
         device_local_account_management_policy_provider_;
     std::unique_ptr<InstallGate> kiosk_app_update_install_gate_;
 #endif
 
     OneShotEvent ready_;
+    void LoadExtensionsFromCommandLineFlag(

[Devlin, 2016/07/27 17:01:00]

Two notes here:
If we were to add this method, we should follow the declaration order style:
https://google.github.io/styleguide/cppguide.html#Declaration_Order (at least
for the most part).  Specifically, methods before members.
That said, I think we can probably do away with this method.  See .cc file.

[catmullings, 2016/08/04 22:59:31]

Moved this definition to extension_service.h. 

[catmullings, 2016/08/04 22:59:31]

Done.

+        const base::CommandLine* command_line,
+        const char* switch_name);
   };
 
   Profile* profile_;
 
   Shared* shared_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionSystemImpl);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SYSTEM_IMPL_H_