Add a policy for disabling the stripping of PAC URLs.

chrome/browser/io_thread.h

Index: chrome/browser/io_thread.h
diff --git a/chrome/browser/io_thread.h b/chrome/browser/io_thread.h
index d6fff0794518dc406b3cebaecd4c2b381b067e16..5a0b3ed3071b2b7612a34c9ebde6ce839158035b 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -238,6 +238,10 @@ class IOThread : public content::BrowserThreadDelegate {
   // Un-registers the |observer|.
   void UnregisterSTHObserver(net::ct::STHObserver* observer);
 
+  // Returns true if the indicated proxy resolution features are enabled.

[mmenke, 2016/06/03 15:59:22]

Do we document these features anywhere in the source?  We don't in the prefs
file, we don't here, and we don't in ProxyServiceFactory::CreateProxyService. 
Think they should be documented somewhere, and have a pointer to that
documentation here.

[eroman, 2016/06/03 16:49:03]

Done.

+  bool WpadQuickCheckEnabled() const;
+  bool PacHttpsUrlStrippingEnabled() const;
+
  private:
   // Provide SystemURLRequestContextGetter with access to
   // InitSystemRequestContext().
@@ -328,6 +332,8 @@ class IOThread : public content::BrowserThreadDelegate {
 
   BooleanPrefMember quick_check_enabled_;
 
+  BooleanPrefMember pac_https_url_stripping_enabled_;
+
   // Store HTTP Auth-related policies in this thread.
   // TODO(aberent) Make the list of auth schemes a PrefMember, so that the
   // policy can change after startup (https://crbug/549273).