Web Locks API: Fix IDL glitch

A callback defined in Web IDL should take a nullable argument. We
don't enforce this in our bindings code and it can't be introspected
from JS so this is not a testable or web-facing change, just aligning
the code with a spec fix.

Spec issue: https://github.com/WICG/web-locks/issues/51
Spec link: https://wicg.github.io/web-locks/#callbackdef-lockgrantedcallback

Change-Id: Icc2e076f62e45629a283d0039e2be30b4a6826c4
Reviewed-on: https://chromium-review.googlesource.com/c/1294421
Commit-Queue: Joshua Bell <jsbell@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601716}

third_party/WebKit/LayoutTests/external/wpt/web-locks/web-locks.idl

@@ -16,7 +16,7 @@ interface LockManager {
   Promise<LockManagerSnapshot> query();
 };
 
-callback LockGrantedCallback = Promise<any> (Lock lock);
+callback LockGrantedCallback = Promise<any> (Lock? lock);
 
 enum LockMode { "shared", "exclusive" };
 

third_party/blink/renderer/modules/locks/lock_manager.idl

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 // https://wicg.github.io/web-locks/#callbackdef-lockgrantedcallback
-callback LockGrantedCallback = any (Lock lock);
+callback LockGrantedCallback = any (Lock? lock);
 
 // https://wicg.github.io/web-locks/#lockmanager
 [