Fix linkHeader tests

Update some title descriptions and provide a proper stylesheet
resource for link-dnsprefetch-in-css.html.

Bug: 456173
Change-Id: I06d2982ded73d6be1e1c9a829c764e3e4a4dfc90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2002871Reviewed-by: Yoav Weiss <yoavweiss@chromium.org>
Commit-Queue: Rob Buis <rbuis@igalia.com>
Cr-Commit-Position: refs/heads/master@{#732836}

third_party/blink/web_tests/http/tests/linkHeader/link-dnsprefetch-in-css-expected.txt

 CONSOLE DEBUG: DNS prefetch triggered for wut.com.test
-This test checks if a Link header inside an iframe triggered a dns prefetch.
+This test checks if a Link header inside a stylesheet triggered a dns prefetch.

third_party/blink/web_tests/http/tests/linkHeader/link-dnsprefetch-in-css.html

@@ -7,6 +7,6 @@
     if (window.internals) {
         internals.settings.setLogDnsPrefetchAndPreconnect(true);
     }
-    document.write("<link rel='stylesheet' href='resources/link-dnsprefetch-image.php' onload='if (window.testRunner)testRunner.notifyDone()'>");
+    document.write("<link rel='stylesheet' href='resources/link-dnsprefetch-css.php' onload='if (window.testRunner)testRunner.notifyDone()'>");
 </script>
-This test checks if a Link header inside an iframe triggered a dns prefetch.
+This test checks if a Link header inside a stylesheet triggered a dns prefetch.

third_party/blink/web_tests/http/tests/linkHeader/link-dnsprefetch-in-image-expected.txt

 CONSOLE DEBUG: DNS prefetch triggered for wut.com.test
- This test checks if a Link header inside an iframe triggered a dns prefetch.
+ This test checks if a Link header inside an image triggered a dns prefetch.

third_party/blink/web_tests/http/tests/linkHeader/link-dnsprefetch-in-image.html

@@ -9,4 +9,4 @@
     }
     document.write("<img src='resources/link-dnsprefetch-image.php' onload='if (window.testRunner)testRunner.notifyDone()'>");
 </script>
-This test checks if a Link header inside an iframe triggered a dns prefetch.
+This test checks if a Link header inside an image triggered a dns prefetch.

third_party/blink/web_tests/http/tests/linkHeader/link-dnsprefetch-in-script-expected.txt

 CONSOLE DEBUG: DNS prefetch triggered for wut.com.test
-This test checks if a Link header inside an iframe triggered a dns prefetch.
+This test checks if a Link header inside a script triggered a dns prefetch.

third_party/blink/web_tests/http/tests/linkHeader/link-dnsprefetch-in-script.html

@@ -9,4 +9,4 @@
     }
     document.write("<script src='resources/link-dnsprefetch-script.php'></s"+"cript>");
 </script>
-This test checks if a Link header inside an iframe triggered a dns prefetch.
+This test checks if a Link header inside a script triggered a dns prefetch.

third_party/blink/web_tests/http/tests/linkHeader/resources/link-dnsprefetch-css.php

+<?php
+header("Link: <   http://wut.com.test/>; rel=dns-prefetch");
+header("Content-Type: text/css");
+?>
+div { }