Instrument cached collection renders.

Augments the collection caching with some instrumentation that's logged.

For collections that have been cached like:

```ruby
<%= render partial: 'notifications/notification', collection: @notifications, cached: true %>
```

We'll output a line showing how many cache hits we had when rendering it:

```
  Rendered collection of notifications/_notification.html.erb [0 / 100 cache hits] (3396.5ms)
```

1 files changed, 17 insertions, 3 deletions

diff --git a/actionview/test/template/log_subscriber_test.rb b/actionview/test/template/log_subscriber_test.rb
index 4776c18b0b..93a0701dcc 100644
--- a/actionview/test/template/log_subscriber_test.rb
+++ b/actionview/test/template/log_subscriber_test.rb
@@ -86,7 +86,7 @@ class AVLogSubscriberTest < ActiveSupport::TestCase
       wait
 
       assert_equal 1, @logger.logged(:info).size
-      assert_match(/Rendered test\/_customer.erb/, @logger.logged(:info).last)
+      assert_match(/Rendered collection of test\/_customer.erb \[2 times\]/, @logger.logged(:info).last)
     end
   end
 
@@ -96,7 +96,7 @@ class AVLogSubscriberTest < ActiveSupport::TestCase
       wait
 
       assert_equal 1, @logger.logged(:info).size
-      assert_match(/Rendered customers\/_customer\.html\.erb/, @logger.logged(:info).last)
+      assert_match(/Rendered collection of customers\/_customer\.html\.erb \[2 times\]/, @logger.logged(:info).last)
     end
   end
 
@@ -106,7 +106,21 @@ class AVLogSubscriberTest < ActiveSupport::TestCase
       wait
 
       assert_equal 1, @logger.logged(:info).size
-      assert_match(/Rendered collection/, @logger.logged(:info).last)
+      assert_match(/Rendered collection of templates/, @logger.logged(:info).last)
+    end
+  end
+
+  def test_render_collection_with_cached_set
+    Rails.stub(:root, File.expand_path(FIXTURE_LOAD_PATH)) do
+      def @view.view_cache_dependencies; []; end
+      def @view.fragment_cache_key(*); 'ahoy `controller` dependency'; end
+
+      @view.render(partial: 'customers/customer', collection: [ Customer.new('david'), Customer.new('mary') ], cached: true,
+        locals: { greeting: 'hi' })
+      wait
+
+      assert_equal 1, @logger.logged(:info).size
+      assert_match(/Rendered collection of customers\/_customer\.html\.erb \[0 \/ 2 cache hits\]/, @logger.logged(:info).last)
     end
   end
 end