[Prerender] Restore request priorities when swapped in

chrome/browser/prerender/prerender_resource_throttle.h

 // Copyright 2013 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_PRERENDER_PRERENDER_RESOURCE_THROTTLE_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_RESOURCE_THROTTLE_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "base/optional.h"
 #include "chrome/common/prerender_types.h"
 #include "content/public/browser/resource_request_info.h"
 #include "content/public/browser/resource_throttle.h"
 #include "content/public/common/resource_type.h"
+#include "net/base/request_priority.h"
 
 class GURL;
 
 namespace net {
 class URLRequest;
 }
 
 namespace prerender {
 class PrerenderContents;
 class PrerenderThrottleInfo;
@@ skipping 16 matching lines @@
   void WillStartRequest(bool* defer) override;
   void WillRedirectRequest(const net::RedirectInfo& redirect_info,
                            bool* defer) override;
   void WillProcessResponse(bool* defer) override;
   const char* GetNameForLogging() const override;
 
   // Called by the PrerenderContents when a prerender becomes visible.
   // May only be called if currently throttling the resource.
   void ResumeHandler();
 
+  // Resets the resource priority back to its original value.
+  void ResetResourcePriority();
+
   static void OverridePrerenderContentsForTesting(PrerenderContents* contents);
 
  private:
   static void WillStartRequestOnUI(
       const base::WeakPtr<PrerenderResourceThrottle>& throttle,
       const std::string& method,
       content::ResourceType resource_type,
       const GURL& url,
       const content::ResourceRequestInfo::WebContentsGetter&
           web_contents_getter,
@@ skipping 20 matching lines @@
   static PrerenderContents* PrerenderContentsFromGetter(
       const content::ResourceRequestInfo::WebContentsGetter&
           web_contents_getter);
 
   // Sets the prerender mode. Must be called before |ResumeHandler()|.
   void SetPrerenderMode(PrerenderMode mode);
 
   net::URLRequest* request_;
   int load_flags_;  // Load flags to be OR'ed with the existing request flags.
 
+  // The throttle changes most request priorities to IDLE during prerendering.
+  // The priority is reset back to the original priority when prerendering is
+  // finished.
+  base::Optional<net::RequestPriority> original_request_priority_;
+
   scoped_refptr<PrerenderThrottleInfo> prerender_throttle_info_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderResourceThrottle);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_RESOURCE_THROTTLE_H_