[NoStatePrefetch] Cancel repeated prefetches with FINAL_STATUS_DUPLICATE

As opposed to a full prerender, a prefetch could be repeated relatively soon.
This CL prevent this by detecting repeated prefetches and cancelling them with
FINAL_STATUS_DUPLICATE.

The threshold used is net::HttpCache::kPrefetchReuseMins (5 minutes), which
should roughly match what is happening for full prerenders.

Review-Url: https://codereview.chromium.org/2614473002
Cr-Commit-Position: refs/heads/master@{#441397}

chrome/browser/prerender/prerender_manager.cc

@@ -65,6 +65,7 @@
 #include "content/public/browser/web_contents_delegate.h"
 #include "content/public/common/url_constants.h"
 #include "extensions/common/constants.h"
+#include "net/http/http_cache.h"
 #include "net/http/http_request_headers.h"
 #include "ui/gfx/geometry/rect.h"
 
@@ -575,6 +576,7 @@ void PrerenderManager::RecordNoStateFirstContentfulPaint(const GURL& url,
   base::TimeDelta prefetch_age;
   Origin origin;
   GetPrefetchInformation(url, &prefetch_age, &origin);
+  OnPrefetchUsed(url);
 
   histograms_->RecordPrefetchFirstContentfulPaintTime(
       origin, is_no_store, was_hidden, time, prefetch_age);
@@ -599,8 +601,8 @@ void PrerenderManager::RecordPrerenderFirstContentfulPaint(
   base::TimeDelta prefetch_age;
   // The origin at prefetch is superceeded by the tab_helper origin for the
   // histogram recording, below.
-  Origin unused_origin;
-  GetPrefetchInformation(url, &prefetch_age, &unused_origin);
+  GetPrefetchInformation(url, &prefetch_age, nullptr);
+  OnPrefetchUsed(url);
 
   base::TimeTicks swap_ticks = tab_helper->swap_ticks();
   bool fcp_recorded = false;
@@ -939,7 +941,17 @@ std::unique_ptr<PrerenderHandle> PrerenderManager::AddPrerender(
     return nullptr;
   }
 
-  if (PrerenderData* preexisting_prerender_data =
+  if (IsNoStatePrefetch(origin)) {
+    base::TimeDelta prefetch_age;
+    GetPrefetchInformation(url, &prefetch_age, nullptr);
+    if (!prefetch_age.is_zero() &&
+        prefetch_age <
+            base::TimeDelta::FromMinutes(net::HttpCache::kPrefetchReuseMins)) {
+      RecordFinalStatusWithoutCreatingPrerenderContents(url, origin,
+                                                        FINAL_STATUS_DUPLICATE);
+      return nullptr;
+    }
+  } else if (PrerenderData* preexisting_prerender_data =
                  FindPrerenderData(url, session_storage_namespace)) {
     RecordFinalStatusWithoutCreatingPrerenderContents(
         url, origin, FINAL_STATUS_DUPLICATE);
@@ -1192,19 +1204,22 @@ void PrerenderManager::GetPrefetchInformation(const GURL& url,
                                               base::TimeDelta* prefetch_age,
                                               Origin* origin) {
   DCHECK(prefetch_age);
-  DCHECK(origin);
   CleanUpOldNavigations(&prefetches_, base::TimeDelta::FromMinutes(30));
 
   *prefetch_age = base::TimeDelta();
+  if (origin)
     *origin = ORIGIN_NONE;
   for (auto it = prefetches_.crbegin(); it != prefetches_.crend(); ++it) {
     if (it->url == url) {
       *prefetch_age = GetCurrentTimeTicks() - it->time;
+      if (origin)
         *origin = it->origin;
       break;
     }
   }
+}
 
+void PrerenderManager::OnPrefetchUsed(const GURL& url) {
   // Loading a prefetched URL resets the revalidation bypass. Remove all
   // matching urls from the prefetch list for more accurate metrics.
   prefetches_.erase(

chrome/browser/prerender/prerender_manager.h

@@ -540,10 +540,15 @@ class PrerenderManager : public content::NotificationObserver,
   void DeleteOldWebContents();
 
   // Get information associated with a possible prefetch of |url|.
+  // |origin| may be null, in which case the origin is not returned.
   void GetPrefetchInformation(const GURL& url,
                               base::TimeDelta* prefetch_age,
                               Origin* origin);
 
+  // Called when a prefetch has been used. Prefetches avoid cache revalidation
+  // only once.
+  void OnPrefetchUsed(const GURL& url);
+
   // Cleans up old NavigationRecord's.
   void CleanUpOldNavigations(std::vector<NavigationRecord>* navigations,
                              base::TimeDelta max_age);

chrome/browser/prerender/prerender_unittest.cc

@@ -38,6 +38,7 @@
 #include "content/public/browser/render_view_host.h"
 #include "content/public/test/test_browser_thread.h"
 #include "net/base/network_change_notifier.h"
+#include "net/http/http_cache.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
@@ -781,6 +782,37 @@ TEST_F(PrerenderTest, LinkManagerNavigateAwayLaunchAnother) {
             prerender_manager()->FindEntry(second_url));
 }
 
+// Prefetching the same URL twice during |time_to_live| results in a duplicate
+// and is aborted.
+TEST_F(PrerenderTest, NoStatePrefetchDuplicate) {
+  const GURL kUrl("http://www.google.com/");
+
+  RestorePrerenderMode restore_prerender_mode;
+  prerender_manager()->SetMode(
+      PrerenderManager::PRERENDER_MODE_NOSTATE_PREFETCH);
+  base::SimpleTestTickClock* tick_clock =
+      OverridePrerenderManagerTimeTicks(prerender_manager());
+
+  // Prefetch the url once.
+  prerender_manager()->CreateNextPrerenderContents(
+      kUrl, ORIGIN_OMNIBOX, FINAL_STATUS_MANAGER_SHUTDOWN);
+  EXPECT_TRUE(
+      prerender_manager()->AddPrerenderFromOmnibox(kUrl, nullptr, gfx::Size()));
+
+  prerender_manager()->CreateNextPrerenderContents(
+      kUrl, ORIGIN_OMNIBOX, FINAL_STATUS_MANAGER_SHUTDOWN);
+
+  // Prefetching again before time_to_live aborts, because it is a duplicate.
+  tick_clock->Advance(base::TimeDelta::FromSeconds(1));
+  EXPECT_FALSE(
+      prerender_manager()->AddPrerenderFromOmnibox(kUrl, nullptr, gfx::Size()));
+
+  // Prefetching after time_to_live succeeds.
+  tick_clock->Advance(
+      base::TimeDelta::FromMinutes(net::HttpCache::kPrefetchReuseMins));
+  EXPECT_TRUE(
+      prerender_manager()->AddPrerenderFromOmnibox(kUrl, nullptr, gfx::Size()));
+}
 
 // Make sure that if we prerender more requests than we support, that we launch
 // them in the order given up until we reach MaxConcurrency, at which point we