Adding a finch param for preconnect experiment

This param does not change the default behavior, but allows adjusting
behavior via finch. This will allow us to modify pre-connect retry
behavior to be slightly less aggressive.

Bug: 964089
Change-Id: I989c075c733e1d5edb5d0b070abcda86acd57545
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1614706Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Auto-Submit: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661024}

chrome/browser/navigation_predictor/navigation_predictor.cc

@@ -136,8 +136,7 @@ NavigationPredictor::NavigationPredictor(
           base::GetFieldTrialParamByFeatureAsBool(
               blink::features::kNavigationPredictor,
               "same_origin_preconnecting_allowed",
-              false))
-{
+              false)) {
   DCHECK(browser_context_);
   DETACH_FROM_SEQUENCE(sequence_checker_);
   DCHECK_LE(0, preconnect_origin_score_threshold_);
@@ -317,14 +316,24 @@ void NavigationPredictor::MaybePreconnectNow(Action log_action) {
   if (current_visibility_ != content::Visibility::VISIBLE)
     return;
 
-  // Set/Reset the timer to fire after the pre-connect times out. Add an extra
-  // 50ms to make sure the preconnect has expired if it wasn't used.
+  // The delay beyond the idle socket timeout that net uses when
+  // re-preconnecting. If negative, no retries occur.
+  int retry_delay_ms = base::GetFieldTrialParamByFeatureAsInt(
+      blink::features::kNavigationPredictor, "retry_preconnect_wait_time_ms",
+      50);
+
+  if (retry_delay_ms < 0) {
+    return;
+  }
+
+  // Set/Reset the timer to fire after the preconnect times out. Add an extra
+  // delay to make sure the preconnect has expired if it wasn't used.
   timer_.Start(
       FROM_HERE,
       base::TimeDelta::FromSeconds(base::GetFieldTrialParamByFeatureAsInt(
           net::features::kNetUnusedIdleSocketTimeout,
           "unused_idle_socket_timeout_seconds", 10)) +
-          base::TimeDelta::FromMilliseconds(50),
+          base::TimeDelta::FromMilliseconds(retry_delay_ms),
       base::BindOnce(&NavigationPredictor::MaybePreconnectNow,
                      base::Unretained(this), Action::kPreconnectAfterTimeout));
 }

chrome/browser/navigation_predictor/navigation_predictor_browsertest.cc

@@ -396,6 +396,33 @@ IN_PROC_BROWSER_TEST_F(NavigationPredictorBrowserTest,
                        NavigationPredictor::Action::kPreconnectAfterTimeout)));
 }
 
+// Test that we don't preconnect after the last preconnect timed out when
+// retry_preconnect_wait_time_ms is negative.
+IN_PROC_BROWSER_TEST_F(NavigationPredictorBrowserTest,
+                       DISABLE_ON_CHROMEOS(ActionAccuracy_timeout_no_retry)) {
+  base::HistogramTester histogram_tester;
+
+  base::test::ScopedFeatureList scoped_feature_list_net;
+  // -1 would force synchronous retries if retries were not disabled.
+  scoped_feature_list_net.InitAndEnableFeatureWithParameters(
+      net::features::kNetUnusedIdleSocketTimeout,
+      {{"unused_idle_socket_timeout_seconds", "-1"}});
+
+  base::test::ScopedFeatureList scoped_feature_list_predictor;
+  scoped_feature_list_predictor.InitAndEnableFeatureWithParameters(
+      blink::features::kNavigationPredictor,
+      {{"retry_preconnect_wait_time_ms", "-1"}});
+
+  const GURL& url = GetTestURL("/page_with_same_host_anchor_element.html");
+  ui_test_utils::NavigateToURL(browser(), url);
+  WaitForLayout(&histogram_tester);
+
+  EXPECT_EQ(0, histogram_tester.GetBucketCount(
+                   "NavigationPredictor.OnNonDSE.ActionTaken",
+                   static_cast<base::HistogramBase::Sample>(
+                       NavigationPredictor::Action::kPreconnectAfterTimeout)));
+}
+
 // Test that the action accuracy is properly recorded and when same origin
 // preconnections are enabled, then navigation predictor initiates the
 // preconnection.

testing/variations/fieldtrial_testing_config.json

@@ -3101,6 +3101,7 @@
                         "is_url_incremented_scale": "100",
                         "preconnect_skip_link_scores": "true",
                         "ratio_area_scale": "100",
+                        "retry_preconnect_wait_time_ms": "50",
                         "same_origin_preconnecting_allowed": "true",
                         "source_engagement_score_scale": "100",
                         "target_engagement_score_scale": "100",