Wake Lock API: Add checks for feature policy.

Added checks for feature policy attribute. This fixes all feature policy
related tests.

BUG=862460,257511

Change-Id: I6258c41dcca164f7c6584ba4a387860237ca3ba3
Reviewed-on: https://chromium-review.googlesource.com/c/1343193
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Mrunal Kapade <mrunal.kapade@intel.com>
Cr-Commit-Position: refs/heads/master@{#615985}

wake-lock/wakelock-enabled-on-self-origin-by-feature-policy.https.sub.html

@@ -12,8 +12,8 @@
   const cross_origin_src =
     "https://{{domains[www]}}:{{ports[https][0]}}" + same_origin_src;
 
-  promise_test(() => {
-    navigator.getWakeLock("screen");
+  promise_test(t => {
+    return navigator.getWakeLock("screen");
   }, 'Feature-Policy header wake-lock "self" allows the top-level document.');
 
   async_test(t => {