Disable NoScript preview by default.

Change-Id: I3bd8fd7ecaf0393848ec91296dacc8996251a14d
Bug: 1090417
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2236679
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Michael Crouse <mcrouse@chromium.org>
Reviewed-by: Sophie Chang <sophiechang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#776373}

components/previews/content/previews_decider_impl_unittest.cc

@@ -860,22 +860,11 @@ TEST_F(PreviewsDeciderImplTest, NoScriptFeatureDefaultBehavior) {
   PreviewsUserData user_data(kDefaultPageId);
   content::MockNavigationHandle navigation_handle;
   navigation_handle.set_url(GURL("https://www.google.com"));
-#if defined(OS_ANDROID)
-  // Enabled by default on Android. NOSCRIPT always allowed at navigation start
-  // to handle asynchronous loading of page hints; non-allowlisted ones are
-  // later blocked on commit.
-  EXPECT_TRUE(previews_decider_impl()->ShouldAllowPreviewAtNavigationStart(
-      &user_data, &navigation_handle, false, PreviewsType::NOSCRIPT));
-  histogram_tester.ExpectTotalCount("Previews.EligibilityReason.NoScript", 1);
-  histogram_tester.ExpectBucketCount(
-      "Previews.EligibilityReason.NoScript",
-      static_cast<int>(PreviewsEligibilityReason::ALLOWED), 1);
-#else   // !defined(OS_ANDROID)
+
   // Disabled by default on non-Android.
   EXPECT_FALSE(previews_decider_impl()->ShouldAllowPreviewAtNavigationStart(
       &user_data, &navigation_handle, false, PreviewsType::NOSCRIPT));
   histogram_tester.ExpectTotalCount("Previews.EligibilityReason.NoScript", 0);
-#endif  // defined(OS_ANDROID)
 }
 
 TEST_F(PreviewsDeciderImplTest, NoScriptNotAllowedWithoutOptimizationHints) {

components/previews/core/previews_features.cc

@@ -29,11 +29,7 @@ const base::Feature kOfflinePreviews{"OfflinePreviews",
 // Support for enabling NoScript previews which includes a base feature
 // and a UserConsistent-specific experiment feature.
 const base::FeatureState kNoScriptDefaultFeatureState =
-#if defined(OS_ANDROID)
-    base::FEATURE_ENABLED_BY_DEFAULT;
-#else   // !defined(OS_ANDROID)
     base::FEATURE_DISABLED_BY_DEFAULT;
-#endif  // defined(OS_ANDROID)
 const base::Feature kNoScriptPreviews{"NoScriptPreviews",
                                       kNoScriptDefaultFeatureState};
 const base::Feature kNoScriptPreviewsUserConsistentStudy{