[MBI] Use per-AgentSchedulingGroup task runners for AgentSchedulingGroup's mojo interfaces

Context:

For MBI, per-AgentSchedulingGroup task runners should be used where appropriate.

What this CL does:

Use per-AgentSchedulingGroup task runners for AgentSchedulingGroup's mojo interfaces instead of per-thread task runners.

Bug: 1105403
Change-Id: I67b6e21e353808ea2b922a1bb1480f62f73feae4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2497868Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Minoru Chikamune <chikamune@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821062}

content/renderer/agent_scheduling_group.cc

@@ -212,11 +212,10 @@ void AgentSchedulingGroup::CreateFrameProxy(
 void AgentSchedulingGroup::BindAssociatedRouteProvider(
     mojo::PendingAssociatedRemote<mojom::RouteProvider> remote,
     mojo::PendingAssociatedReceiver<mojom::RouteProvider> receiver) {
-  remote_route_provider_.Bind(std::move(remote));
+  remote_route_provider_.Bind(std::move(remote),
+                              agent_group_scheduler_->DefaultTaskRunner());
   route_provider_receiver_.Bind(std::move(receiver),
-                                ToImpl(render_thread_)
-                                    .GetWebMainThreadScheduler()
-                                    ->DeprecatedDefaultTaskRunner());
+                                agent_group_scheduler_->DefaultTaskRunner());
 }
 
 void AgentSchedulingGroup::GetRoute(
@@ -224,8 +223,9 @@ void AgentSchedulingGroup::GetRoute(
     mojo::PendingAssociatedReceiver<blink::mojom::AssociatedInterfaceProvider>
         receiver) {
   DCHECK(receiver.is_valid());
-  associated_interface_provider_receivers_.Add(this, std::move(receiver),
-                                               routing_id);
+  associated_interface_provider_receivers_.Add(
+      this, std::move(receiver), routing_id,
+      agent_group_scheduler_->DefaultTaskRunner());
 }
 
 void AgentSchedulingGroup::GetAssociatedInterface(