Update links to layout test documentation.

docs/layout_tests_linux.md

 # Running layout tests on Linux
 
 1.  Build `blink_tests` (see [Linux-specific build instructions](https://chromium.googlesource.com/chromium/src/+/master/docs/linux_build_instructions.md))
 1.  Checkout the layout tests
     *   If you have an entry in your `.gclient` file that includes
         "LayoutTests", you may need to comment it out and sync.
     *   You can run a subset of the tests by passing in a path relative to
         `src/third_party/WebKit/LayoutTests/`.  For example,
         `run_layout_tests.py fast` will only run the tests under
         `src/third_party/WebKit/LayoutTests/fast/`.
 1.  When the tests finish, any unexpected results should be displayed.
 
-See
-[Running WebKit Layout Tests](http://dev.chromium.org/developers/testing/webkit-layout-tests)
+See [Layout Tests](testing/layout_tests.md)
 for full documentation about set up and available options.
 
 ## Pixel Tests
 
 The pixel test results were generated on Ubuntu 10.4 (Lucid). If you're running
 a newer version of Ubuntu, you will get some pixel test failures due to changes
 in freetype or fonts.  In this case, you can create a Lucid 64 chroot using
 `build/install-chroot.sh` to compile and run tests.
 
 ## Fonts
@@ skipping 104 matching lines @@
 In your `.xmonad/xmonad.hs`, change your config to include a manageHook along
 these lines:
 
 ```
 test_shell_manage = className =? "Test_shell" --> doFloat
 main = xmonad $
   defaultConfig
     { manageHook = test_shell_manage <+> manageHook defaultConfig
     ...
 ```