Minor fixes for layout test writing documentation.

The main reason for this CL is to change the recommended path for
accessing testharness.js from HTTP tests. The file can be accessed using
both the old path (/js-test-resources/testharness.js) and the new path
(/resources/testharness.js). However, our testharnessresult.js uses the
CSS selector script[src*="/resources/testharness"] to identify
JavaScript tests, causing tests that use the old path to fail without a
text baseline.

The CL also adds an "under construction" unicode character to the
guideline for adding a <meta charset> to every test, as it is still
under discussion.

BUG=

Review-Url: https://codereview.chromium.org/2579953002
Cr-Commit-Position: refs/heads/master@{#439266}
diff --git a/docs/testing/writing_layout_tests.md b/docs/testing/writing_layout_tests.md
index 7067687c..f2767c2 100644
--- a/docs/testing/writing_layout_tests.md
+++ b/docs/testing/writing_layout_tests.md
@@ -270,8 +270,9 @@
 
 ### Character Encoding
 
-Tests should use the UTF-8 **character encoding**, which should be declared by
-`<meta charset=utf-8>`. This does not apply when specifically testing encodings.
+&#x1F6A7; Tests should use the UTF-8 **character encoding**, which should be
+declared by `<meta charset=utf-8>`. This does not apply when specifically
+testing encodings.
 
 The `<meta>` tag must be the first child of the document's `<head>` element. In
 documents that do not have an explicit `<head>`, the `<meta>` tag must follow
@@ -653,7 +654,7 @@
 
 The test server sets up an alias to the `LayoutTests/resources` directory. In
 HTTP tests, you can access the testing framework at e.g.
-`src="/js-test-resources/testharness.js"`.
+`src="/resources/testharness.js"`.
 
 TODO: Document [wptserve](http://wptserve.readthedocs.io/) when we are in a
 position to use it to run layout tests.