Explicitly mark LazyBackgroundTaskQueue non-copyable.

We neither copy LazyBackgroundTaskQueue instances, nor we need to.
Delete its copy operators.

Bug: None
Change-Id: I759fe181e9c1d561769922b299043463fe7e5cd0
Reviewed-on: https://chromium-review.googlesource.com/1036613
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567487}

extensions/browser/lazy_background_task_queue.h

@@ -122,6 +122,8 @@ class LazyBackgroundTaskQueue : public KeyedService,
 
   ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver>
       extension_registry_observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(LazyBackgroundTaskQueue);
 };
 
 }  // namespace extensions