[MBI] Use per-AgentSchedulingGroup task runners for AssociatedInterfaceProvider

Previously, AssociatedInterfaceProvider was using per-thread task runners implicitly. This CL specifies per-Agent task runners.

Bug: 1105403
Change-Id: I14adef7939c48916e1d239482dbeaa19e03e8c9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2505258Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Minoru Chikamune <chikamune@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822498}

content/renderer/render_frame_proxy.cc

@@ -742,7 +742,9 @@ RenderFrameProxy::GetRemoteAssociatedInterfaces() {
         routing_id_, remote_interfaces.InitWithNewEndpointAndPassReceiver());
     remote_associated_interfaces_ =
         std::make_unique<blink::AssociatedInterfaceProvider>(
-            std::move(remote_interfaces));
+            std::move(remote_interfaces),
+            agent_scheduling_group_.agent_group_scheduler()
+                .DefaultTaskRunner());
   }
   return remote_associated_interfaces_.get();
 }