Add WebUSB layout tests for device disconnection.

third_party/WebKit/LayoutTests/usb/usb.html

Index: third_party/WebKit/LayoutTests/usb/usb.html
diff --git a/third_party/WebKit/LayoutTests/usb/usb.html b/third_party/WebKit/LayoutTests/usb/usb.html
index 4a2ca697eca0d95114dfbdaea326d1210136fe56..51aa29b38ede3743eb941cffb9e3c3549ddb8cc1 100644
--- a/third_party/WebKit/LayoutTests/usb/usb.html
+++ b/third_party/WebKit/LayoutTests/usb/usb.html
@@ -17,13 +17,22 @@ usb_test(usb => {
 }, 'getDevices returns devices exposed by the DeviceManager service.');
 
 usb_test(usb => {
+  return navigator.usb.requestDevice({ filters: [] })
+    .then(device => {
+      assert_unreachable('requestDevice should reject without a user gesture');
+    })
+    .catch(error => {
+      assert_equals(error.code, DOMException.SECURITY_ERR);
+    });
+}, 'requestDevice rejects when called without a user gesture');
+
+usb_test(usb => {
   return callWithKeyDown(() => navigator.usb.requestDevice({ filters: [] })
     .then(device => {
       assert_unreachable('requestDevice should reject when no device selected');
     })
     .catch(error => {
       assert_equals(error.code, DOMException.NOT_FOUND_ERR);
-      return Promise.resolve();
     })
   );
 }, 'requestDevice rejects when no device is chosen');