[MBI] Remove IPCTaskRunner usage on AgentMetricsCollector

We are going to remove ipc_task_queue and ipc_task_runner. The scheduling policy of ipc_task_queue is the same as the default task queue. Nowadays, we are using per-frame task queues as much as possible. And if there are no relevant per-frame task queues, then we can use the (per-isolate) default task queues.

[related design doc section]
https://docs.google.com/document/d/1y-vHkrD1z2RtyWYwT6rJkSLHClYNjDDpUbTtBU7l95A/edit#bookmark=id.eeuir8g768ou

Bug: 1105403
Change-Id: I5da4bd5434f92f714d49f0beb9bec4e6b7588cb4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2332106Reviewed-by: Tal Pressman <talp@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Minoru Chikamune <chikamune@chromium.org>
Cr-Commit-Position: refs/heads/master@{#794870}

third_party/blink/renderer/core/execution_context/agent_metrics_collector.cc

@@ -166,7 +166,7 @@ AgentMetricsCollector::GetAgentMetricsCollectorHost() {
   if (!agent_metrics_collector_host_.is_bound()) {
     blink::Platform::Current()->GetBrowserInterfaceBroker()->GetInterface(
         agent_metrics_collector_host_.BindNewPipeAndPassReceiver(
-            ThreadScheduler::Current()->IPCTaskRunner()));
+            ThreadScheduler::Current()->DeprecatedDefaultTaskRunner()));
   }
   return agent_metrics_collector_host_.get();
 }