Add Virtual Keyboard bordered key experiment to chrome flag

BUG: b/143232594

Change-Id: I76b160ad565649db32a21b984fbed1594b0ae6ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1875347
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: My Nguyen <myy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710190}
  FlagsStateSingleton()
      : flags_state_(std::make_unique<flags_ui::FlagsState>(
            kFeatureEntries,
            base::size(kFeatureEntries),
            base::Bind(&FlagsStateSingleton::IsFlagExpired))) {}

  FlagsStateSingleton()
      : flags_state_(std::make_unique<flags_ui::FlagsState>(
            kFeatureEntries,
            base::size(kFeatureEntries),
            base::Bind(&FlagsStateSingleton::IsFlagExpired))) {}
