Revert "removing Rack::Runtime from the default stack."

This reverts commit 37423e4ff883ad5584bab983aceb4b2b759a1fd8.

Jeremy is right that we shouldn't remove this.  The fact is that many
engines are depending on this middleware to be in the default stack.
This ties our hands and forces us to keep the middleware in the stack so
that engines will work.  To be extremely clear, I think this is another
smell of "the rack stack" that we have in place.  When manipulating
middleware, we should have meaningful names for places in the req / res
lifecycle **not** have engines depend on a particular constant be in a
particular place in the stack.  This is a weakness of the API that we
have to figure out a way to address before removing the constant.

As far as timing attacks are concerned, we can reduce the granularity
such that it isn't useful information for hackers, but is still useful
for developers.

3 files changed, 3 insertions, 1 deletions

diff --git a/guides/source/api_app.md b/guides/source/api_app.md
index eb762612ee..feaaff166a 100644
--- a/guides/source/api_app.md
+++ b/guides/source/api_app.md
@@ -188,6 +188,7 @@ An API application comes with the following middlewares by default:
 - `ActiveSupport::Cache::Strategy::LocalCache::Middleware`
 - `ActionDispatch::RequestId`
 - `Rails::Rack::Logger`
+- `Rack::Runtime`
 - `ActionDispatch::ShowExceptions`
 - `ActionDispatch::DebugExceptions`
 - `ActionDispatch::RemoteIp`
diff --git a/guides/source/command_line.md b/guides/source/command_line.md
index cbfccce788..e85f9fc9c6 100644
--- a/guides/source/command_line.md
+++ b/guides/source/command_line.md
@@ -412,7 +412,7 @@ Ruby version              2.2.2 (x86_64-linux)
 RubyGems version          2.4.6
 Rack version              1.6
 JavaScript Runtime        Node.js (V8)
-Middleware                Rack::Sendfile, ActionDispatch::Static, Rack::Lock, #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x007ffd131a7c88>, Rack::MethodOverride, ActionDispatch::RequestId, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::DebugExceptions, ActionDispatch::RemoteIp, ActionDispatch::Reloader, ActionDispatch::Callbacks, ActiveRecord::Migration::CheckPending, ActiveRecord::ConnectionAdapters::ConnectionManagement, ActiveRecord::QueryCache, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, Rack::Head, Rack::ConditionalGet, Rack::ETag
+Middleware                Rack::Sendfile, ActionDispatch::Static, Rack::Lock, #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x007ffd131a7c88>, Rack::Runtime, Rack::MethodOverride, ActionDispatch::RequestId, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::DebugExceptions, ActionDispatch::RemoteIp, ActionDispatch::Reloader, ActionDispatch::Callbacks, ActiveRecord::Migration::CheckPending, ActiveRecord::ConnectionAdapters::ConnectionManagement, ActiveRecord::QueryCache, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, Rack::Head, Rack::ConditionalGet, Rack::ETag
 Application root          /home/foobar/commandsapp
 Environment               development
 Database adapter          sqlite3
diff --git a/guides/source/rails_on_rack.md b/guides/source/rails_on_rack.md
index 1479e6f263..87f869aff3 100644
--- a/guides/source/rails_on_rack.md
+++ b/guides/source/rails_on_rack.md
@@ -106,6 +106,7 @@ use Rack::Sendfile
 use ActionDispatch::Static
 use Rack::Lock
 use #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x000000029a0838>
+use Rack::Runtime
 use Rack::MethodOverride
 use ActionDispatch::RequestId
 use Rails::Rack::Logger