Require a user gesture to use navigator.share.

third_party/WebKit/LayoutTests/webshare/resources/mock-share-service.js

 'use strict';
 
 let mockShareService = loadMojoModules(
     'mockShareService',
     ['mojo/public/js/router',
      'third_party/WebKit/public/platform/modules/webshare/webshare.mojom',
     ]).then(mojo => {
   let [router, webshare] = mojo.modules;
 
   class MockShareService extends webshare.ShareService.stubClass {
@@ skipping 46 matching lines @@
   }
   return new MockShareService(mojo.frameInterfaces);
 });
 
 function share_test(func, name, properties) {
   promise_test(t => mockShareService.then(mock => {
     let mockPromise = mock.init_();
     return Promise.race([func(t, mock), mockPromise]);
   }), name, properties);
 }
+
+// Copied from resources/bluetooth/bluetooth-helpers.js.
+function callWithKeyDown(functionCalledOnKeyPress) {
+  return new Promise(resolve => {
+    function onKeyPress() {
+      document.removeEventListener('keypress', onKeyPress, false);
+      resolve(functionCalledOnKeyPress());
+    }
+    document.addEventListener('keypress', onKeyPress, false);
+
+    eventSender.keyDown(' ', []);
+  });
+}