[WPT] Use `self` to access global object in testharness

This is to run testharness.js as module scripts (e.g. via `import`).

For the same purpose, this CL also fixes undeclared variable
in Chromium's testharnessreport.js.

Bug: https://github.com/web-platform-tests/wpt/issues/12480
Change-Id: I1ff539676b754e27c9f5d50a355f5ca2fb9c07b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2341230Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796696}

third_party/blink/web_tests/external/wpt/resources/testharness.js

@@ -3998,5 +3998,5 @@ span.ok, span.timeout, span.error {\
 }\
 ";
 
-})(this);
+})(self);
 // vim: set expandtab shiftwidth=4 tabstop=4:

third_party/blink/web_tests/resources/testharnessreport.js

@@ -174,7 +174,7 @@
         }
 
         // Output failure metrics if there are many.
-        resultCounts = countResultTypes(tests);
+        const resultCounts = countResultTypes(tests);
         if (outputDocument.URL.indexOf('://web-platform.test') >= 0 &&
             tests.length >= 50 &&
             (resultCounts[1] || resultCounts[2] || resultCounts[3])) {