Introduce Feature Policy: vertical-scroll (bare feature)

This CL introduces the bare feature. 'vertical-scroll' intends to block
specific sandboxed frames (which do not have the feature enabled) from
interfering with user's vertical scrolling in the page. The details are
explained in the document:

https://docs.google.com/document/d/1qiWelnMlsOHuT_CQ0Zm_qEAf54HS5DhoIvEDHBlfqps/edit?usp=sharing

The actual logic for blocking such frames will land in follow-up CLs.

Bug: 611982
Change-Id: I17bfc3e421cda06c4cba40efb6de046bed66bd14
Reviewed-on: https://chromium-review.googlesource.com/1007843Reviewed-by: Ian Clelland <iclelland@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Rick Byers <rbyers@chromium.org>
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550254}

third_party/blink/common/feature_policy/feature_policy.cc

@@ -285,6 +285,8 @@ const FeaturePolicy::FeatureList& FeaturePolicy::GetDefaultFeatureList() {
                            {mojom::FeaturePolicyFeature::kUnsizedMedia,
                             FeaturePolicy::FeatureDefault::EnableForAll},
                            {mojom::FeaturePolicyFeature::kPictureInPicture,
+                            FeaturePolicy::FeatureDefault::EnableForAll},
+                           {mojom::FeaturePolicyFeature::kVerticalScroll,
                             FeaturePolicy::FeatureDefault::EnableForAll}}));
   return default_feature_list;
 }

third_party/blink/public/mojom/feature_policy/feature_policy.mojom

@@ -83,6 +83,8 @@ enum FeaturePolicyFeature {
   kUnsizedMedia,
   // Controls access to Picture-in-Picture.
   kPictureInPicture,
+  // Controls the ability to block and interfere with vertical scrolling.
+  kVerticalScroll,
 };
 
 // This struct holds feature policy whitelist data that needs to be replicated

third_party/blink/renderer/platform/feature_policy/feature_policy.cc

@@ -216,6 +216,8 @@ bool IsSupportedInFeaturePolicy(mojom::FeaturePolicyFeature feature) {
       return true;
     case mojom::FeaturePolicyFeature::kUnsizedMedia:
       return RuntimeEnabledFeatures::FeaturePolicyExperimentalFeaturesEnabled();
+    case mojom::FeaturePolicyFeature::kVerticalScroll:
+      return RuntimeEnabledFeatures::FeaturePolicyExperimentalFeaturesEnabled();
     default:
       return false;
   }
@@ -268,6 +270,8 @@ const FeatureNameMap& GetDefaultFeatureNameMap() {
                                    mojom::FeaturePolicyFeature::kSyncScript);
       default_feature_name_map.Set("unsized-media",
                                    mojom::FeaturePolicyFeature::kUnsizedMedia);
+      default_feature_name_map.Set(
+          "vertical-scroll", mojom::FeaturePolicyFeature::kVerticalScroll);
     }
     if (RuntimeEnabledFeatures::FeaturePolicyAutoplayFeatureEnabled()) {
       default_feature_name_map.Set("autoplay",