[headless_tests OS_WIN] Added kNoSandbox switch to headless tests.

Adding this flag prevents sandbox_type.cc complaining about valid
sandbox configuration missing in a command line.

Change-Id: I076aaf51411c187e36f3b08f6eb5e50199b2b804
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2446656
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Auto-Submit: Peter Kvitek <kvitekp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813429}

headless/lib/headless_content_main_delegate.cc

@@ -231,6 +231,7 @@ bool HeadlessContentMainDelegate::BasicStartupComplete(int* exit_code) {
   command_line->AppendSwitch(::blink::switches::kAllowPreCommitInput);
 
 #if defined(OS_WIN)
+  command_line->AppendSwitch(sandbox::policy::switches::kNoSandbox);
   command_line->AppendSwitch(
       ::switches::kDisableGpuProcessForDX12InfoCollection);
 #endif