Add build flags to control building Feed V2 with Chrome Modern

Bug: 1115463
Change-Id: I29b0658596cd5c9c10ea2832435cca7a873f6ee4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510914Reviewed-by: Clark DuVall <cduvall@chromium.org>
Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Ian Wells <iwells@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823636}

components/feed/features.gni

@@ -15,6 +15,12 @@ declare_args() {
 
   # Whether version 2 of the NTP feed is enabled in the build.
   enable_feed_v2 = is_android
+
+  # Whether to include Feed V2 in ChromeModern builds.
+  enable_feed_v2_modern = false
+
+  # Whether to include Feed V2 as a DFM in ChromeModern builds.
+  dfmify_feed_v2_modern = false
 }
 
 if (is_android && android_channel != "default") {