Make performance bar enabled checks consistent

Previously, we called the `peek_enabled?` method like so:

    prepend_before_action :set_peek_request_id, if: :peek_enabled?

Now we don't have a `set_peek_request_id` method, so we don't need that
line. However, the `peek_enabled?` part had a side-effect: it would also
populate the request store cache for whether the performance bar was
enabled for the current request or not.

This commit makes that side-effect explicit, and replaces all uses of
`peek_enabled?` with the more explicit
`Gitlab::PerformanceBar.enabled_for_request?`. There is one spec that
still sets `SafeRequestStore[:peek_enabled]` directly, because it is
contrasting behaviour with and without a request store enabled.

The upshot is:

1. We still set the value in one place. We make it more explicit that
   that's what we're doing.
2. Reading that value uses a consistent method so it's easier to find in
   future.

1 files changed, 1 insertions, 3 deletions

diff --git a/app/helpers/performance_bar_helper.rb b/app/helpers/performance_bar_helper.rb
index 7518cec160c..b225e4206a9 100644
--- a/app/helpers/performance_bar_helper.rb
+++ b/app/helpers/performance_bar_helper.rb
@@ -1,9 +1,7 @@
 # frozen_string_literal: true
 
 module PerformanceBarHelper
-  # This is a hack since using `alias_method :performance_bar_enabled?, :peek_enabled?`
-  # in WithPerformanceBar breaks tests (but works in the browser).
   def performance_bar_enabled?
-    peek_enabled?
+    Gitlab::PerformanceBar.enabled_for_request?
   end
 end