Disabling Previews on reloads by default

This is being launched to 100% of stable after this CL lands.

Bug: 914029
Change-Id: Iecaeaa54fa404c9f25ae2d8172a3a620ff4533a9
Reviewed-on: https://chromium-review.googlesource.com/c/1490732Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636601}

components/previews/content/previews_decider_impl_unittest.cc

@@ -823,7 +823,7 @@ TEST_F(PreviewsDeciderImplTest, MissingHostDisallowed) {
       &user_data, GURL("file:///sdcard"), false, PreviewsType::LOFI));
 }
 
-TEST_F(PreviewsDeciderImplTest, ClientLoFiAllowedOnReload) {
+TEST_F(PreviewsDeciderImplTest, ClientLoFiDisallowedOnReload) {
   base::test::ScopedFeatureList scoped_feature_list;
   scoped_feature_list.InitWithFeatures(
       {features::kPreviews, features::kClientLoFi}, {});
@@ -836,11 +836,11 @@ TEST_F(PreviewsDeciderImplTest, ClientLoFiAllowedOnReload) {
   PreviewsUserData user_data(kDefaultPageId);
 
   base::HistogramTester histogram_tester;
-  EXPECT_TRUE(previews_decider_impl()->ShouldAllowPreviewAtNavigationStart(
+  EXPECT_FALSE(previews_decider_impl()->ShouldAllowPreviewAtNavigationStart(
       &user_data, GURL("https://www.google.com"), true, PreviewsType::LOFI));
   histogram_tester.ExpectUniqueSample(
       "Previews.EligibilityReason.LoFi",
-      static_cast<int>(PreviewsEligibilityReason::ALLOWED), 1);
+      static_cast<int>(PreviewsEligibilityReason::RELOAD_DISALLOWED), 1);
 }
 
 TEST_F(PreviewsDeciderImplTest, NoScriptFeatureDefaultBehavior) {

components/previews/core/previews_features.cc

@@ -98,7 +98,7 @@ const base::Feature kSlowPageTriggering{"PreviewsSlowPageTriggering",
 
 // A feature to prevent previews on all reloads.
 const base::Feature kPreviewsDisallowedOnReloads{
-    "PreviewsDisallowedOnReloads", base::FEATURE_DISABLED_BY_DEFAULT};
+    "PreviewsDisallowedOnReloads", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Allows HTTPS previews to be served via a URLLoader when network service is
 // enabled.

testing/variations/fieldtrial_testing_config.json

@@ -3738,21 +3738,6 @@
             ]
         }
     ],
-    "PreviewsDisallowedOnReloads": [
-        {
-            "platforms": [
-                "android"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "PreviewsDisallowedOnReloads"
-                    ]
-                }
-            ]
-        }
-    ],
     "PreviewsLitePageRedirect": [
         {
             "platforms": [