Fix query cache to load before first request

In a test app we observed that the query cache was not enabled on the
first request. This was because the query cache hooks are installed on
load and active record is loaded in the middle of the first request.

If we remove the `on_load` from the railtie the query cache hooks will
be installed before the first request, allowing the cache to be enabled
on that first request.

This is ok because query cache doesn't load anything else, only itself
so we're not eager loading all of active record before the first
request, just the query cache hooks.

[Eileen M. Uchitelle & Matthew Draper]

activerecord/lib/active_record/railtie.rb

@@ -180,9 +180,7 @@ class Railtie < Rails::Railtie # :nodoc:
     end
 
     initializer "active_record.set_executor_hooks" do
-      ActiveSupport.on_load(:active_record) do
-        ActiveRecord::QueryCache.install_executor_hooks
-      end
+      ActiveRecord::QueryCache.install_executor_hooks
     end
 
     initializer "active_record.add_watchable_files" do |app|

railties/test/application/loading_test.rb

@@ -371,6 +371,39 @@ def test_initialize_can_be_called_at_any_time
     end
   end
 
+  test "active record query cache hooks are installed before first request" do
+    app_file "app/controllers/omg_controller.rb", <<-RUBY
+      begin
+        class OmgController < ActionController::Metal
+          ActiveSupport.run_load_hooks(:action_controller, self)
+          def show
+            if ActiveRecord::Base.connection.query_cache_enabled
+              self.response_body = ["Query cache is enabled."]
+            else
+              self.response_body = ["Expected ActiveRecord::Base.connection.query_cache_enabled to be true"]
+            end
+          end
+        end
+      rescue => e
+        puts "Error loading metal: \#{e.class} \#{e.message}"
+      end
+    RUBY
+
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+        get "/:controller(/:action)"
+      end
+    RUBY
+
+    require "#{rails_root}/config/environment"
+
+    require "rack/test"
+    extend Rack::Test::Methods
+
+    get "/omg/show"
+    assert_equal "Query cache is enabled.", last_response.body
+  end
+
   private
 
     def setup_ar!