[Previews] Increases default slow page trigger max threshold to 3G

Bug: 895581, 879906
Change-Id: If67cbc221834449b84c2c9491890e06afa10f138
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1666911Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Doug Arnett <dougarnett@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672235}

components/previews/core/previews_experiments.cc

@@ -322,7 +322,7 @@ net::EffectiveConnectionType GetECTThresholdForPreview(
 net::EffectiveConnectionType GetSessionMaxECTThreshold() {
   return GetParamValueAsECTByFeature(features::kSlowPageTriggering,
                                      kSessionMaxECTTrigger,
-                                     net::EFFECTIVE_CONNECTION_TYPE_2G);
+                                     net::EFFECTIVE_CONNECTION_TYPE_3G);
 }
 
 bool ArePreviewsAllowed() {

testing/variations/fieldtrial_testing_config.json

@@ -4145,24 +4145,6 @@
             ]
         }
     ],
-    "PreviewsSlowPageTriggering": [
-        {
-            "platforms": [
-                "android"
-            ],
-            "experiments": [
-                {
-                    "name": "SlowPageTriggeringFor4G_20190312",
-                    "params": {
-                        "session_max_ect_trigger": "4G"
-                    },
-                    "enable_features": [
-                        "PreviewsSlowPageTriggering"
-                    ]
-                }
-            ]
-        }
-    ],
     "PrioritizedSimpleCacheTasks": [
         {
             "platforms": [