GestureNavigation: Turn on the feature by default

In preparation of 100% stable rollout, this CL turns on the feature
by default, and deletes the field trial configuration.

Bug: 1128629, 1006111
Change-Id: I03b8af9c5a3bbcb2b5ff20b567c86366e3122217
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2561910
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832138}

content/public/common/content_features.cc

@@ -456,14 +456,8 @@ const base::Feature kOpenXrExtendedFeatureSupport{
     "OpenXrExtendedFeatureSupport", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // History navigation in response to horizontal overscroll (aka gesture-nav).
-const base::Feature kOverscrollHistoryNavigation {
-  "OverscrollHistoryNavigation",
-#if defined(OS_ANDROID)
-      base::FEATURE_DISABLED_BY_DEFAULT
-#else
-      base::FEATURE_ENABLED_BY_DEFAULT
-#endif
-};
+const base::Feature kOverscrollHistoryNavigation{
+    "OverscrollHistoryNavigation", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Whether web apps can run periodic tasks upon network connectivity.
 const base::Feature kPeriodicBackgroundSync{"PeriodicBackgroundSync",

testing/variations/fieldtrial_testing_config.json

@@ -3135,22 +3135,6 @@
             ]
         }
     ],
-    "GestureNavigation": [
-        {
-            "platforms": [
-                "android",
-                "android_weblayer"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "OverscrollHistoryNavigation"
-                    ]
-                }
-            ]
-        }
-    ],
     "GlobalMediaControlsInProductHelp": [
         {
             "platforms": [