Mojo: Fix wrapping of invalid SharedMemoryHandles.

components/discardable_memory/public/interfaces/discardable_shared_memory_manager.mojom

Index: components/discardable_memory/public/interfaces/discardable_shared_memory_manager.mojom
diff --git a/components/discardable_memory/public/interfaces/discardable_shared_memory_manager.mojom b/components/discardable_memory/public/interfaces/discardable_shared_memory_manager.mojom
index 2685be1cd57cdec954c5de484a7b6e12f3c93d21..9d291d82d22a64a7cd2f353ab966e64f056660ca 100644
--- a/components/discardable_memory/public/interfaces/discardable_shared_memory_manager.mojom
+++ b/components/discardable_memory/public/interfaces/discardable_shared_memory_manager.mojom
@@ -10,7 +10,7 @@ interface DiscardableSharedMemoryManager {
   // Allocate a locked discardable shared memory segment.
   AllocateLockedDiscardableSharedMemory(
       uint32 size,
-      int32 id) => (handle<shared_buffer> memory);
+      int32 id) => (handle<shared_buffer>? memory);
   // Notify manager that a memory segment has been deleted.
   DeletedDiscardableSharedMemory(int32 id);
 };