Fix http/tests/preload/meta-viewport-device-width-link-headers.html

It was flaky because the path to slow-script.pl was wrong.

This narrows the failure expectation only to
virtual/synchronous_html_parser, where viewport-dependent preloads don't
work because DispatchLinkHeaderPreloads() from
HTMLDocumentParser::EnqueueTokenizedChunk() is not called.

Bug: 944025,901056
Change-Id: Ib76f9367a1eb5ab73ab1c81e40c60b9e331488e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2279295Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786121}

third_party/blink/web_tests/TestExpectations

@@ -80,6 +80,7 @@ external/wpt/css/compositing/root-element-background-transparency.html [ Failure
 
 ### virtual/synchronous_html_parser/http/tests/preload/
 crbug.com/901056 virtual/synchronous_html_parser/http/tests/preload/meta-csp.html [ Failure ]
+crbug.com/901056 virtual/synchronous_html_parser/http/tests/preload/meta-viewport-device-width-link-headers.html [ Failure ]
 crbug.com/901056 virtual/synchronous_html_parser/http/tests/preload/meta-viewport-link-headers-imagesrcset.html [ Timeout Failure ]
 
 # ====== Site Isolation failures from here ======
@@ -5645,7 +5646,6 @@ crbug.com/943969 [ Mac10.11 ] inspector-protocol/css/css-get-media-queries.js [
 crbug.com/945085 [ Mac10.13 ] printing/composited-thead-tfoot-repeat.html [ Failure Pass ]
 
 # Sheriff 2019-03-25
-crbug.com/944025 http/tests/preload/meta-viewport-device-width-link-headers.html [ Pass Failure ]
 crbug.com/945665 http/tests/devtools/elements/styles-3/styles-add-new-rule-tab.js [ Pass Failure ]
 crbug.com/945665 http/tests/devtools/elements/styles-3/styles-add-new-rule.js [ Pass Failure Timeout ]
 crbug.com/945665 http/tests/devtools/elements/styles-3/styles-disable-inherited.js [ Pass Failure ]

third_party/blink/web_tests/http/tests/preload/resources/media-link-headers-device-width.php

@@ -16,8 +16,9 @@
         }
         if (nonzeroLoaded)
             window.opener.postMessage("success", "*")
-        window.opener.postMessage("nonzeronotloaded", "*");
+        else
+            window.opener.postMessage("nonzeronotloaded", "*");
     });
 </script>
-<script src="../resources/slow-script.pl?delay=200"></script>
+<script src="/resources/slow-script.pl?delay=200"></script>