Reland "Adding a FTT config for PreconnectSameOriginDesktop"

This is a reland of 4e23e8e8

Patchset 1 is what previously landed. This caused flakes in other
loading predictor browser tests, so I added the holdback to all
of the tests. In a follow-up, I will make sure the tests check
for preconnects on the appropriate URLs.

See https://chromium-review.googlesource.com/c/chromium/src/+/2004181
for revert rationale.

Original change's description:
> Adding a FTT config for PreconnectSameOriginDesktop
>
> This experiment is in canary/dev and should be moved to Beta.
>
> Bug: 1038774
> Change-Id: I4fc9c44e2b68aa58f9eee7210a625103f45edb01
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1992684
> Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
> Reviewed-by: Alex Ilin <alexilin@chromium.org>
> Reviewed-by: Ilya Sherman <isherman@chromium.org>
> Reviewed-by: Tarun Bansal <tbansal@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#732219}

Bug: 1038774
Change-Id: Id7bd4bddf5b5812d02a8953d0733f8af73007fb6

TBR=tbansal@chromium.org,alexilin@chromium.org

Change-Id: Id7bd4bddf5b5812d02a8953d0733f8af73007fb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2004691Reviewed-by: Alex Ilin <alexilin@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732553}

chrome/browser/navigation_predictor/navigation_predictor_preconnect_client.cc

@@ -23,7 +23,7 @@
 #include "content/public/browser/web_contents.h"
 #include "net/base/features.h"
 
-namespace {
+namespace features {
 
 // A holdback that prevents the preconnect to measure benefit of the feature.
 const base::Feature kNavigationPredictorPreconnectHoldback {
@@ -34,6 +34,9 @@ const base::Feature kNavigationPredictorPreconnectHoldback {
       base::FEATURE_ENABLED_BY_DEFAULT
 #endif
 };
+}  // namespace features
+
+namespace {
 
 // Experiment with which event triggers the preconnect after commit.
 const base::Feature kPreconnectOnDidFinishNavigation{
@@ -110,7 +113,8 @@ void NavigationPredictorPreconnectClient::DidFinishLoad(
 }
 
 void NavigationPredictorPreconnectClient::MaybePreconnectNow() {
-  if (base::FeatureList::IsEnabled(kNavigationPredictorPreconnectHoldback))
+  if (base::FeatureList::IsEnabled(
+          features::kNavigationPredictorPreconnectHoldback))
     return;
 
   if (browser_context_->IsOffTheRecord())

chrome/browser/navigation_predictor/navigation_predictor_preconnect_client.h

@@ -19,6 +19,10 @@ class BrowserContext;
 class RenderFrameHost;
 }  // namespace content
 
+namespace features {
+extern const base::Feature kNavigationPredictorPreconnectHoldback;
+}
+
 class NavigationPredictorPreconnectClient
     : public content::WebContentsObserver,
       public content::WebContentsUserData<NavigationPredictorPreconnectClient> {

chrome/browser/predictors/loading_predictor_browsertest.cc

@@ -19,6 +19,7 @@
 #include "base/task/post_task.h"
 #include "base/test/scoped_feature_list.h"
 #include "chrome/browser/browser_features.h"
+#include "chrome/browser/navigation_predictor/navigation_predictor_preconnect_client.h"
 #include "chrome/browser/predictors/loading_predictor.h"
 #include "chrome/browser/predictors/loading_predictor_factory.h"
 #include "chrome/browser/predictors/loading_test_util.h"
@@ -444,7 +445,8 @@ class LoadingPredictorBrowserTest : public InProcessBrowserTest {
   LoadingPredictorBrowserTest() {
     scoped_feature_list_.InitWithFeatures(
         {features::kLoadingOnlyLearnHighPriorityResources,
-         features::kLoadingPreconnectToRedirectTarget},
+         features::kLoadingPreconnectToRedirectTarget,
+         features::kNavigationPredictorPreconnectHoldback},
         {});
   }
   ~LoadingPredictorBrowserTest() override {}

testing/variations/OWNERS

 file://base/metrics/OWNERS
 
+# Use the following owners only if:
+#  - You work in the same area as them.
+#  - They are already aware of the field trial being modified.
+per-file fieldtrial_testing_config.json=tbansal@chromium.org
+
 # COMPONENT: Internals>Metrics>Variations

testing/variations/fieldtrial_testing_config.json

@@ -4958,6 +4958,30 @@
             ]
         }
     ],
+    "PreconnectSameOriginDesktop": [
+        {
+            "platforms": [
+                "windows",
+                "chromeos",
+                "mac",
+                "linux"
+            ],
+            "experiments": [
+                {
+                    "name": "EnabledWithExtendedSocket",
+                    "params": {
+                        "unused_idle_socket_timeout_seconds": "60"
+                    },
+                    "enable_features": [
+                        "NetUnusedIdleSocketTimeout"
+                    ],
+                    "disable_features": [
+                        "NavigationPredictorPreconnectHoldback"
+                    ]
+                }
+            ]
+        }
+    ],
     "PrefetchSRPAndroid": [
         {
             "platforms": [