Use allow attribute for delegation in generic sensor WPT

With an upcoming change to Feature/Permissions Policy, the header
alone will no longer be sufficient to delegate permissions to use
powerful features in subframes. The iframe allow attribute must
be used in conjunction with it. The header can still be used to
block delegation.

This change updates the generic sensor WPTs to use the allow
attribute for delegation.

Bug: 1095641
Change-Id: I7ba5512c755816e5072dcb4aade3e13f4904456f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2424654
Commit-Queue: Ian Clelland <iclelland@chromium.org>
Auto-Submit: Ian Clelland <iclelland@chromium.org>
Reviewed-by: Charlie Hu <chenleihu@google.com>
Cr-Commit-Position: refs/heads/master@{#809845}

third_party/blink/web_tests/external/wpt/generic-sensor/generic-sensor-feature-policy-test.sub.js

@@ -72,13 +72,16 @@ function run_fp_tests_enabled(sensorName) {
     );
   }, `${sensorName}: ${header} allows same-origin iframes.`);
 
+  // Set allow="feature;feature;..." on iframe element to delegate features
+  // under test to cross origin subframe.
   async_test(t => {
     assert_implements(sensorName in self, `${sensorName} is not supported.`);
     test_feature_availability(
       desc,
       t,
       cross_origin_src + sensorName,
-      expect_feature_available_default
+      expect_feature_available_default,
+      feature_policies[sensorName].join(";")
     );
   }, `${sensorName}: ${header} allows cross-origin iframes.`);
 }