Limit number of IsolatedPrerender prefetches on experiment params

Defaults to 1.

Bug: 1023485
Change-Id: Ia76fe2e0150b60f3a4e15b5bcdb674de63899c5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2025570
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736194}

chrome/browser/prerender/isolated/isolated_prerender_params.cc

@@ -36,3 +36,18 @@ bool IsolatedPrerenderShouldReplaceDataReductionCustomProxy() {
   DCHECK(!replace);
   return replace;
 }
+
+base::Optional<size_t> IsolatedPrerenderMaximumNumberOfPrefetches() {
+  if (!base::FeatureList::IsEnabled(
+          features::kPrefetchSRPNavigationPredictions_HTMLOnly)) {
+    return 0;
+  }
+
+  int max = base::GetFieldTrialParamByFeatureAsInt(
+      features::kPrefetchSRPNavigationPredictions_HTMLOnly,
+      "max_srp_prefetches", 1);
+  if (max < 0) {
+    return base::nullopt;
+  }
+  return max;
+}

chrome/browser/prerender/isolated/isolated_prerender_params.h

@@ -5,6 +5,8 @@
 #ifndef CHROME_BROWSER_PRERENDER_ISOLATED_ISOLATED_PRERENDER_PARAMS_H_
 #define CHROME_BROWSER_PRERENDER_ISOLATED_ISOLATED_PRERENDER_PARAMS_H_
 
+#include <stdint.h>
+
 #include "base/optional.h"
 #include "url/gurl.h"
 
@@ -18,4 +20,9 @@ base::Optional<GURL> IsolatedPrerenderProxyServer();
 // custom proxy.
 bool IsolatedPrerenderShouldReplaceDataReductionCustomProxy();
 
+// The maximum number of prefetches that should be done from predictions on a
+// Google SRP. nullopt is returned for unlimited. Negative values given by the
+// field trial return nullopt.
+base::Optional<size_t> IsolatedPrerenderMaximumNumberOfPrefetches();
+
 #endif  // CHROME_BROWSER_PRERENDER_ISOLATED_ISOLATED_PRERENDER_PARAMS_H_

chrome/browser/prerender/isolated/isolated_prerender_tab_helper.cc

@@ -10,6 +10,7 @@
 #include "base/feature_list.h"
 #include "chrome/browser/navigation_predictor/navigation_predictor_keyed_service_factory.h"
 #include "chrome/browser/prerender/isolated/isolated_prerender_features.h"
+#include "chrome/browser/prerender/isolated/isolated_prerender_params.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.h"
 #include "components/google/core/common/google_util.h"
@@ -88,6 +89,7 @@ void IsolatedPrerenderTabHelper::DidFinishNavigation(
   DCHECK(!PrefetchingActive());
   urls_to_prefetch_.clear();
   prefetched_responses_.clear();
+  num_prefetches_attempted_ = 0;
 }
 
 std::unique_ptr<PrefetchedResponseContainer>
@@ -115,6 +117,13 @@ void IsolatedPrerenderTabHelper::Prefetch() {
   if (urls_to_prefetch_.empty())
     return;
 
+  if (IsolatedPrerenderMaximumNumberOfPrefetches().has_value() &&
+      num_prefetches_attempted_ >=
+          IsolatedPrerenderMaximumNumberOfPrefetches().value()) {
+    return;
+  }
+  num_prefetches_attempted_++;
+
   GURL url = urls_to_prefetch_[0];
   urls_to_prefetch_.erase(urls_to_prefetch_.begin());
 
@@ -230,6 +239,15 @@ void IsolatedPrerenderTabHelper::OnPredictionUpdated(
     return;
   }
 
+  // This is also checked before prefetching from the network, but checking
+  // again here allows us to skip querying for cookies if we won't be
+  // prefetching the url anyways.
+  if (IsolatedPrerenderMaximumNumberOfPrefetches().has_value() &&
+      num_prefetches_attempted_ >=
+          IsolatedPrerenderMaximumNumberOfPrefetches().value()) {
+    return;
+  }
+
   if (!prediction.has_value()) {
     return;
   }

chrome/browser/prerender/isolated/isolated_prerender_tab_helper.h

@@ -5,6 +5,7 @@
 #ifndef CHROME_BROWSER_PRERENDER_ISOLATED_ISOLATED_PRERENDER_TAB_HELPER_H_
 #define CHROME_BROWSER_PRERENDER_ISOLATED_ISOLATED_PRERENDER_TAB_HELPER_H_
 
+#include <stdint.h>
 #include <map>
 #include <memory>
 #include <vector>
@@ -96,6 +97,9 @@ class IsolatedPrerenderTabHelper
   // An ordered list of the URLs to prefetch.
   std::vector<GURL> urls_to_prefetch_;
 
+  // The number of prefetches that have been attempted on this page.
+  size_t num_prefetches_attempted_ = 0;
+
   // All prefetched responses by URL. This is cleared every time a mainframe
   // navigation commits.
   std::map<GURL, std::unique_ptr<PrefetchedResponseContainer>>

chrome/browser/prerender/isolated/isolated_prerender_tab_helper_unittest.cc

@@ -394,3 +394,67 @@ TEST_F(IsolatedPrerenderTabHelperTest, SuccessCase) {
   network::mojom::URLResponseHeadPtr head = resp->TakeHead();
   EXPECT_TRUE(head->headers->HasHeaderValue("X-Testing", "Hello World"));
 }
+
+TEST_F(IsolatedPrerenderTabHelperTest, LimitedNumberOfPrefetches_Zero) {
+  base::test::ScopedFeatureList scoped_feature_list;
+  scoped_feature_list.InitAndEnableFeatureWithParameters(
+      features::kPrefetchSRPNavigationPredictions_HTMLOnly,
+      {{"max_srp_prefetches", "0"}});
+
+  GURL doc_url("https://www.google.com/search?q=cats");
+  GURL prediction_url("https://www.cat-food.com/");
+  MakeNavigationPrediction(web_contents(), doc_url, {prediction_url});
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_EQ(RequestCount(), 0);
+}
+
+TEST_F(IsolatedPrerenderTabHelperTest, LimitedNumberOfPrefetches_Unlimited) {
+  base::test::ScopedFeatureList scoped_feature_list;
+  scoped_feature_list.InitAndEnableFeatureWithParameters(
+      features::kPrefetchSRPNavigationPredictions_HTMLOnly,
+      {{"max_srp_prefetches", "-1"}});
+
+  GURL doc_url("https://www.google.com/search?q=cats");
+  GURL prediction_url_1("https://www.cat-food.com/");
+  GURL prediction_url_2("https://www.dogs-r-dumb.com/");
+  GURL prediction_url_3("https://www.catz-rule.com/");
+  MakeNavigationPrediction(
+      web_contents(), doc_url,
+      {prediction_url_1, prediction_url_2, prediction_url_3});
+
+  VerifyCommonRequestState(prediction_url_1);
+  MakeResponseAndWait(net::HTTP_OK, net::OK, kHTMLMimeType, {}, kHTMLBody);
+  VerifyCommonRequestState(prediction_url_2);
+  // Failed responses do not retry or attempt more requests in the list.
+  MakeResponseAndWait(net::HTTP_OK, net::ERR_FAILED, kHTMLMimeType, {},
+                      kHTMLBody);
+  VerifyCommonRequestState(prediction_url_3);
+  MakeResponseAndWait(net::HTTP_OK, net::OK, kHTMLMimeType, {}, kHTMLBody);
+
+  EXPECT_EQ(RequestCount(), 0);
+}
+
+TEST_F(IsolatedPrerenderTabHelperTest, LimitedNumberOfPrefetches) {
+  base::test::ScopedFeatureList scoped_feature_list;
+  scoped_feature_list.InitAndEnableFeatureWithParameters(
+      features::kPrefetchSRPNavigationPredictions_HTMLOnly,
+      {{"max_srp_prefetches", "2"}});
+
+  GURL doc_url("https://www.google.com/search?q=cats");
+  GURL prediction_url_1("https://www.cat-food.com/");
+  GURL prediction_url_2("https://www.dogs-r-dumb.com/");
+  GURL prediction_url_3("https://www.catz-rule.com/");
+  MakeNavigationPrediction(
+      web_contents(), doc_url,
+      {prediction_url_1, prediction_url_2, prediction_url_3});
+
+  VerifyCommonRequestState(prediction_url_1);
+  // Failed responses do not retry or attempt more requests in the list.
+  MakeResponseAndWait(net::HTTP_OK, net::ERR_FAILED, kHTMLMimeType, {},
+                      kHTMLBody);
+  VerifyCommonRequestState(prediction_url_2);
+  MakeResponseAndWait(net::HTTP_OK, net::OK, kHTMLMimeType, {}, kHTMLBody);
+
+  EXPECT_EQ(RequestCount(), 0);
+}