Simplify cache hit logging

CacheHelper is mixed in to Helpers, Helpers is mixed in to AV::Base.
This means we can count on instances of AV::Base to have the "cache hit"
method on them, and we can stop setting an ivar for cache logging and
just ask the view if it was a cache hit.

actionview/lib/action_view/helpers/cache_helper.rb

@@ -211,6 +211,8 @@ def cache_fragment_name(name = {}, skip_digest: nil, virtual_path: nil)
         end
       end
 
+      attr_reader :cache_hit # :nodoc:
+
     private
 
       def fragment_name_with_digest(name, virtual_path) #:nodoc:
@@ -224,13 +226,12 @@ def fragment_name_with_digest(name, virtual_path) #:nodoc:
         end
       end
 
-      # TODO: Create an object that has caching read/write on it
       def fragment_for(name = {}, options = nil, &block) #:nodoc:
         if content = read_fragment_for(name, options)
-          @log_payload_for_partial_render[:cache_hit] = true if defined?(@log_payload_for_partial_render)
+          @cache_hit = true
           content
         else
-          @log_payload_for_partial_render[:cache_hit] = false if defined?(@log_payload_for_partial_render)
+          @cache_hit = false
           write_fragment_for(name, options, &block)
         end
       end

actionview/lib/action_view/renderer/partial_renderer.rb

@@ -333,8 +333,6 @@ def render_partial
           view, locals, block = @view, @locals, @block
           object, as = @object, @variable
 
-          view.instance_variable_set(:@log_payload_for_partial_render, payload)
-
           if !block && (layout = @options[:layout])
             layout = find_template(layout.to_s, @template_keys)
           end
@@ -347,6 +345,7 @@ def render_partial
           end
 
           content = layout.render(view, locals) { content } if layout
+          payload[:cache_hit] = view.cache_hit
           content
         end
       end