[Windows Sandbox] Turn on MITIGATION_EXTENSION_POINT_DISABLE for child processes.

content/app/sandbox_helper_win.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/app/sandbox_helper_win.h"
 
 #include "sandbox/win/src/process_mitigations.h"
 #include "sandbox/win/src/sandbox_factory.h"
 
 namespace content {
 
 void InitializeSandboxInfo(sandbox::SandboxInterfaceInfo* info) {
   info->broker_services = sandbox::SandboxFactory::GetBrokerServices();
   if (!info->broker_services) {
     info->target_services = sandbox::SandboxFactory::GetTargetServices();
   } else {
     // Ensure the proper mitigations are enforced for the browser process.
     sandbox::ApplyProcessMitigationsToCurrentProcess(
         sandbox::MITIGATION_DEP |
         sandbox::MITIGATION_DEP_NO_ATL_THUNK |
         sandbox::MITIGATION_HARDEN_TOKEN_IL_POLICY);
+    // Note: these mitigations are "post-startup".  Some mitigations that need
+    // to be enabled sooner (e.g. MITIGATION_EXTENSION_POINT_DISABLE) are done
+    // so in Chrome_ELF.
   }
 }
 
 }  // namespace content