Fix the LoggerSilence to work as described:

- Following the Rails guide which state that a logger needs to include
  the `ActiveSupport::LoggerSilence` as well as
  `ActiveSupport::LoggerThreadSafe` modules isn't enough and won't
  work.

  Here is a test cases with 3 tests that all fails
  https://gist.github.com/Edouard-chin/4a72930c2b1eafbbd72a80c66f102010

  The problems are the following:

  1) The logger needs to call `after_initialize` in order to setup
  some instance variables.
  2) The silence doesn't actually work because the bare ruby Logger
  `add` method checks for the instance variable `@logger`. We need to
  override the `add` (like we used to in the ActiveSupport::Logger
  class).
  3) Calling `debug?` `info?` etc... doesn't work as the bare ruby
  methods will check for the instance variable. Again we need to
  override this methods (like we used to in the ActiveSupport::Logger
  class)

  The LoggerSilence won't work without LoggerThreadSafe, but the later
  is not public API, the user shouldn't have to include it so I
  modified to include it automatically.
  Same for the `after_initialize` method. I find unuintitive to have
  to call it directly. I modified to instance the variables when the
  module get included.

1 files changed, 1 insertions, 2 deletions

diff --git a/guides/source/configuring.md b/guides/source/configuring.md
index d23af2ca57..812565b207 100644
--- a/guides/source/configuring.md
+++ b/guides/source/configuring.md
@@ -119,11 +119,10 @@ defaults to `:debug` for all environments. The available log levels are: `:debug
 * `config.logger` is the logger that will be used for `Rails.logger` and any related Rails logging such as `ActiveRecord::Base.logger`. It defaults to an instance of `ActiveSupport::TaggedLogging` that wraps an instance of `ActiveSupport::Logger` which outputs a log to the `log/` directory. You can supply a custom logger, to get full compatibility you must follow these guidelines:
   * To support a formatter, you must manually assign a formatter from the `config.log_formatter` value to the logger.
   * To support tagged logs, the log instance must be wrapped with `ActiveSupport::TaggedLogging`.
-  * To support silencing, the logger must include `ActiveSupport::LoggerSilence` and `ActiveSupport::LoggerThreadSafeLevel` modules. The `ActiveSupport::Logger` class already includes these modules.
+  * To support silencing, the logger must include `ActiveSupport::LoggerSilence`  module. The `ActiveSupport::Logger` class already includes these modules.
 
     ```ruby
     class MyLogger < ::Logger
-      include ActiveSupport::LoggerThreadSafeLevel
       include ActiveSupport::LoggerSilence
     end