Update links to layout test documentation.

docs/how_to_extend_layout_test_framework.md

 # How to Extend the Layout Test Framework
 
 The Layout Test Framework that Blink uses is a regression testing tool that is
 multi-platform and it has a large amount of tools that help test varying types
 of regression, such as pixel diffs, text diffs, etc. The framework is mainly
 used by Blink, however it was made to be extensible so that other projects can
 use it test different parts of chrome (such as Print Preview). This is a guide
 to help people who want to actually the framework to test whatever they want.
 
 [TOC]
 
 ## Background
 
 Before you can start actually extending the framework, you should be familiar
-with how to use it. This wiki is basically all you need to learn how to use it
-http://www.chromium.org/developers/testing/webkit-layout-tests
+with how to use it. See the
+[layout tests documentation](testing/layout_tests.md).
 
 ## How to Extend the Framework
 
 There are two parts to actually extending framework to test a piece of software.
 The first part is extending certain files in:
 [/third_party/Webkit/Tools/Scripts/webkitpy/layout_tests/](/third_party/Webkit/Tools/Scripts/webkitpy/layout_tests/)
 The code in `webkitpy/layout_tests` is the layout test framework itself
 
 The second part is creating a driver (program) to actually communicate the
 layout test framework. This part is significantly more tricky and dependant on
@@ skipping 95 matching lines @@
     *   It should be overridden to return the driver extension class created
         earlier. This function doesn’t return an instance on the driver, just
         the class itself.
 *   `driver_name`
     *   This should return the name of the program test p. By default it returns
         ‘content_shell’, but you want to have it return the program you want to
         run, such as `chrome` or `browser_tests`.
 *   `layout_tests_dir`
     *   This tells the port where to look for all the and everything associated
         with them such as resources files.
-    *   By default it returns absolute path to the webkit tests.
+    *   By default it returns the absolute path to the layout tests directory.
     *   If you are planning on running something in the chromium src/ directory,
         there are helper functions to allow you to return a path relative to the
         base of the chromium src directory.
 
 The rest of the functions can definitely be overridden for your projects
 specific needs, however these are the bare minimum needed to get it running.
 There are also functions you can override to make certain actions that aren’t on
 by default always take place. For example, the layout test framework always
 checks for system dependencies unless you pass in a switch. If you want them
 disabled for your project, just override `check_sys_deps` to always return OK.
@@ skipping 109 matching lines @@
             *   In this case this is how your output should look.
                 *   “Content-type: image/png\n”
                 *   “ActualHash: hashData\n”
                 *   “Content-Length: lengthOfPng\n”
                 *   “pngdata”
                     *   This part doesn’t need a header specifying that you are
                         sending png data, just send it
                 *   “#EOF\n” on both stdout and stderr
             *   To see the structure of the data required, look at the
                 `read_block` functions in Driver.py