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

Many pages of testthewebforward.org now redirect, so replace links with
something appropriate from the new documentation.

Since the new documentation consistently says "web-platform-tests"
instead of "Web Platform Tests" and this is what folks like jgraham tend
to write as well, align our own usage with that.

BUG=657117

Review-Url: https://codereview.chromium.org/2696323003
Cr-Commit-Position: refs/heads/master@{#451045}
diff --git a/docs/testing/writing_layout_tests.md b/docs/testing/writing_layout_tests.md
index 3ccb369..81146831 100644
--- a/docs/testing/writing_layout_tests.md
+++ b/docs/testing/writing_layout_tests.md
@@ -13,13 +13,12 @@
 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](./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.
+   tests that we contribute to [web-platform-tests](./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),
@@ -74,7 +73,7 @@
 
 Tests should be written under the assumption that they will be upstreamed
 to the WPT project. To this end, tests should follow the
-[WPT guidelines](http://testthewebforward.org/docs/writing-tests.html).
+[WPT guidelines](http://web-platform-tests.org/writing-tests/).
 
 
 There is no style guide that applies to all layout tests. However, some projects
@@ -100,12 +99,12 @@
 which is shared with all the other browser vendors, so `testharness.js` tests
 are more accessible to browser developers.
 
-As a shared framework, `testharness.js` enjoys high-quality documentation, such
-as [a tutorial](http://testthewebforward.org/docs/testharness-tutorial.html) and
-[API documentation](https://github.com/w3c/testharness.js/blob/master/docs/api.md).
-Layout tests should follow the recommendations of the above documents.
+See the [API documentation](https://github.com/w3c/testharness.js/blob/master/docs/api.md)
+for a thorough introduction to `testharness.js`.
+
+Layout tests should follow the recommendations of the above documentation.
 Furthermore, layout tests should include relevant
-[metadata](http://testthewebforward.org/docs/css-metadata.html). The
+[metadata](http://web-platform-tests.org/writing-tests/css-metadata.html). The
 specification URL (in `<link rel="help">`) is almost always relevant, and is
 incredibly helpful to a developer who needs to understand the test quickly.
 
@@ -353,8 +352,8 @@
 cannot be covered by JavaScript tests.
 
 New reference tests should follow the
-[WPT reftests guidelines](http://testthewebforward.org/docs/reftests.html). The
-most important points are summarized below.
+[WPT reftests guidelines](http://web-platform-tests.org/writing-tests/reftests.html).
+The most important points are summarized below.
 
 * &#x1F6A7; The test page declares the reference page using a
   `<link rel="match">` or `<link rel="mismatch">`, depending on whether the test
@@ -426,7 +425,7 @@
 Pixel tests should still follow the principles laid out above. Pixel tests pose
 unique challenges to the desire to have *self-describing* and *cross-platform*
 tests. The
-[WPT test style guidelines](http://testthewebforward.org/docs/test-style-guidelines.html)
+[WPT rendering test guidelines](http://web-platform-tests.org/writing-tests/rendering.html)
 contain useful guidance. The most relevant pieces of advice are below.
 
 * Whenever possible, use a green paragraph / page / square to indicate success.