Experiment to disable Prerendering with fast wind-down

chrome/browser/prerender/prerender_manager.h

 // Copyright (c) 2012 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_MANAGER_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 189 matching lines @@
       const GURL& url);
 
   static PrerenderManagerMode GetMode();
   static void SetMode(PrerenderManagerMode mode);
   static const char* GetModeString();
   static bool IsPrerenderingPossible();
   static bool ActuallyPrerendering();
   static bool IsControlGroup();
   static bool IsNoUseGroup();
   static bool IsNoStatePrefetch();
+  bool IsPrerenderSilenceExperiment();
 
   // Query the list of current prerender pages to see if the given web contents
   // is prerendering a page. The optional parameter |origin| is an output
   // parameter which, if a prerender is found, is set to the Origin of the
   // prerender |web_contents|.
   bool IsWebContentsPrerendering(const content::WebContents* web_contents,
                                  Origin* origin) const;
 
   // Whether the PrerenderManager has an active prerender with the given url and
   // SessionStorageNamespace associated with the given WebContents.
@@ skipping 169 matching lines @@
 
   // Same as base::SysInfo::IsLowEndDevice(), overridden in tests.
   virtual bool IsLowEndDevice() const;
 
  private:
   friend class PrerenderBrowserTest;
   friend class PrerenderContents;
   friend class PrerenderHandle;
   friend class UnitTestPrerenderManager;
 
+  // For testing |AddPrerender()| by iterating via a list of origins.
+  FRIEND_TEST_ALL_PREFIXES(PrerenderTest, PrerenderSilenceDisallowsNonOffline);

[mmenke, 2016/08/25 19:22:50]

I suggest adding a "IsPrerenderSilenceExperimentForTesting" method instead of
friending the test.  Makes what's exposed to tests clearer.

[pasko, 2016/08/26 11:22:12]

Hm, eliminating FRIEND_TEST_ALL_PREFIXES is indeed a good idea, and it seems you
are suggesting _not_ to call AddPrerender in the test (directly or indirectly).

I am hesitating, a simple wrapper AddPrerenderForTesting would allow testing
AddPrerender itself, and not just a method that it maybe-invokes.

OK, I've done what I think you mean, can revert/rework if it reveals more
problematic. PTAL.

+
   class OnCloseWebContentsDeleter;
   struct NavigationRecord;
   using PrerenderDataVector = std::vector<std::unique_ptr<PrerenderData>>;
 
   // Time interval before a new prerender is allowed.
   static const int kMinTimeBetweenPrerendersMs = 500;
 
   // Time window for which we record old navigations, in milliseconds.
   static const int kNavigationRecordWindowMs = 5000;
 
@@ skipping 154 matching lines @@
   // Set of process hosts being prerendered.
   using PrerenderProcessSet = std::set<content::RenderProcessHost*>;
   PrerenderProcessSet prerender_process_hosts_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderManager);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_