WPT: CSS: Add same-origin tests for loading error stylesheets.

This adds a test that a stylesheet that failed to load is considered
cross-origin. That is, accessing |styleSheet.rules| throws a
SecurityError.  This aligns with the specifications:
- cssRules checks the `origin-clean` flag:
  https://drafts.csswg.org/cssom/#dom-cssstylesheet-cssrules
- This is set to true iff CORS-same-origin:
  https://html.spec.whatwg.org/multipage/links.html#link-type-stylesheet
- CORS-same-origin is false for "error" responses:
  https://html.spec.whatwg.org/multipage/urls-and-fetching.html#cors-same-origin

Bug: 911974
Change-Id: I558e6d3dfa564b15284c393ffc35b80f54a9bc4e
Reviewed-on: https://chromium-review.googlesource.com/c/1371307
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615479}

third_party/blink/web_tests/external/wpt/css/cssom/stylesheet-same-origin.sub-expected.txt

@@ -4,6 +4,9 @@ PASS Origin-clean check in cross-origin CSSOM Stylesheets (redirect from same-or
 FAIL Origin-clean check in cross-origin CSSOM Stylesheets (redirect from cross-origin to same-origin) assert_throws: stylesheet.cssRules should throw SecurityError. function "function () {
                     sheet.cssRules;
                 }" did not throw
+FAIL Origin-clean check in loading error CSSOM Stylesheets assert_throws: stylesheet.cssRules should throw SecurityError. function "function () {
+                    sheet.cssRules;
+                }" did not throw
 PASS Origin-clean check in same-origin CSSOM Stylesheets
 PASS Origin-clean check in data:css CSSOM Stylesheets
 Harness: the test ran to completion.

third_party/blink/web_tests/external/wpt/css/cssom/stylesheet-same-origin.sub.html

@@ -16,11 +16,13 @@
     <link id="redirect-crossorigin-to-sameorigin"
           href="http://www1.{{host}}:{{ports[http][1]}}/common/redirect.py?location=http://{{host}}:{{ports[http][0]}}/css/cssom/stylesheet-same-origin.css"
           rel="stylesheet">
+    <link id="loaderror" href="support/malformed-http-response.asis" rel="stylesheet">
 
     <script>
         var crossorigin = document.getElementById("crossorigin").sheet;
         var redirectSameOriginToCrossOrigin = document.getElementById("redirect-sameorigin-to-crossorigin").sheet;
         var redirectCrossOriginToSameOrigin = document.getElementById("redirect-crossorigin-to-sameorigin").sheet;
+        var loadError = document.getElementById("loaderror").sheet;
         var sameorigin = document.getElementById("sameorigin").sheet;
         var sameorigindata = document.getElementById("sameorigindata").sheet;
 
@@ -63,6 +65,10 @@
             doOriginDirtyCheck(redirectCrossOriginToSameOrigin);
         }, "Origin-clean check in cross-origin CSSOM Stylesheets (redirect from cross-origin to same-origin)");
 
+       test(function() {
+            doOriginDirtyCheck(loadError);
+        }, "Origin-clean check in loading error CSSOM Stylesheets");
+
         test(function() {
             doOriginCleanCheck(sameorigin, "Same-origin");
         }, "Origin-clean check in same-origin CSSOM Stylesheets");

third_party/blink/web_tests/external/wpt/css/cssom/support/malformed-http-response.asis

+HAHAHA THIS IS NOT HTTP AND THE BROWSER SHOULD CONSIDER IT A NETWORK ERROR