Link to web_platform_tests.md where appropriate

R=qyearsley@chromium.org,rbyers@chromium.org

Review-Url: https://codereview.chromium.org/2689843002
Cr-Commit-Position: refs/heads/master@{#449799}

docs/testing/layout_tests.md

@@ -464,11 +464,10 @@ 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.
 
-## W3C Tests
+## Web Platform Tests
 
-In addition to layout tests developed and run just by the Blink team, there are
-also W3C conformance tests. For more info, see
-[Importing the W3C Tests](https://www.chromium.org/blink/importing-the-w3c-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).
 
 ## Known Issues
 

docs/testing/writing_layout_tests.md

@@ -14,12 +14,12 @@ Layout tests should be used to accomplish one of the following goals:
 
 1. The entire surface of Blink that is exposed to the Web should be covered by
    tests that we contribute to the
-   [Web Platform Tests Project](https://github.com/w3c/web-platform-tests)
-   (WPT). This helps us avoid regressions, and helps us identify Web Platform
-   areas where the major browsers don't have interoperable implementations.
-   Furthermore, by contributing to projects such as WPT, we share the burden of
-   writing tests with the other browser vendors, and we help all the browsers
-   get better. This is very much in line with our goal to move the Web forward.
+   [Web Platform Tests Project](./web_platform_tests.md) (WPT). This helps us
+   avoid regressions, and helps us identify Web Platform areas where the major
+   browsers don't have interoperable implementations. Furthermore, by
+   contributing to projects such as WPT, we share the burden of writing tests
+   with the other browser vendors, and we help all the browsers get better. This
+   is very much in line with our goal to move the Web forward.
 2. When a Blink feature cannot be tested using the tools provided by WPT, and
    cannot be easily covered by
    [C++ unit tests](https://cs.chromium.org/chromium/src/third_party/WebKit/Source/web/tests/?q=webframetest&sq=package:chromium&type=cs),