Link to new web-platform-tests.org documentation from our own

docs/testing/layout_tests.md

 # Layout Tests
 
 Layout tests are used by Blink to test many components, including but not
 limited to layout and rendering. In general, layout tests involve loading pages
 in a test renderer (`content_shell`) and comparing the rendered output or
 JavaScript output against an expected output file.
 
 This document covers running and debugging existing layout tests. See the
 [Writing Layout Tests documentation](./writing_layout_tests.md) if you find
 yourself writing layout tests.
@@ skipping 446 matching lines @@
 The above command will generate a new baseline for
 `LayoutTests/foo/bar/test.html` and put the output files in the right place,
 e.g.
 `LayoutTests/platform/chromium-win/LayoutTests/foo/bar/test-expected.{txt,png,checksum}`.
 
 When you rebaseline a test, make sure your commit description explains why the
 test is being re-baselined. If this is a special case (i.e., something we've
 decided to be different with upstream), please put a README file next to the new
 expected output explaining the difference.
 
-## Web Platform Tests
+## web-platform-tests
 
 In addition to layout tests developed and run just by the Blink team, there is
-also a shared test suite, see [Web Platform Tests](./web_platform_tests.md).
+also a shared test suite, see [web-platform-tests](./web_platform_tests.md).
 
 ## Known Issues
 
 See
 [bugs with the component Blink>Infra](https://bugs.chromium.org/p/chromium/issues/list?can=2&q=component%3ABlink%3EInfra)
 for issues related to Blink tools, include the layout test runner.
 
 * Windows and Linux: Do not copy and paste while the layout tests are running,
   as it may interfere with the editing/pasteboard and other clipboard-related
   tests. (Mac tests swizzle NSClipboard to avoid any conflicts).
 * If QuickTime is not installed, the plugin tests
   `fast/dom/object-embed-plugin-scripting.html` and
   `plugins/embed-attributes-setting.html` are expected to fail.