CSP: "local schemes" should inherit policy when embedded.

third_party/WebKit/LayoutTests/http/tests/security/contentSecurityPolicy/resources/cascade-helper.js

+function assert_allowed_image_in_document(test, doc, url) {
+  doc.addEventListener('securitypolicyviolation', test.step_func(e => {
+    if (e.blockedURI == url)
+      assert_unreached("No violation expected for " + url);
+  }));
+
+  var i = doc.createElement('img');
+  i.onerror = test.unreached_func("onerror fired for " + url);
+  i.onload = test.step_func_done();
+  i.src = url;
+}
+
+
+function assert_blocked_image_in_document(test, doc, url) {
+  var cspEvent = false;
+  var errorEvent = false;
+  doc.addEventListener('securitypolicyviolation', test.step_func(e => {
+    if (e.blockedURI != url)
+      return;
+
+    cspEvent = true;
+    if (errorEvent)
+      test.done();
+  }));
+
+  var i = doc.createElement('img');
+  i.onload = test.unreached_func("onload fired for " + url);
+  i.onerror = test.step_func(e => {
+    errorEvent = true;
+    if (cspEvent)
+      test.done();
+  });
+  i.src = url;
+}