Pass approprite task runners to AssociatedBinding::Bind via RenderThreadImpl

This is part of efforts to replace base::ThreadTaskRunnerHandle::Get()
and SequencedTaskRunnerHandle::Get() with other appropriate task runners
in the renderer.

Bug: 786332
Change-Id: Ibabee0c19403e3a2b1273f9b98eb6ca7f1d114a3
Reviewed-on: https://chromium-review.googlesource.com/980095Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546006}

content/renderer/render_thread_impl.cc

@@ -2637,7 +2637,8 @@ void RenderThreadImpl::OnTrimMemoryImmediately() {
 void RenderThreadImpl::OnRendererInterfaceRequest(
     mojom::RendererAssociatedRequest request) {
   DCHECK(!renderer_binding_.is_bound());
-  renderer_binding_.Bind(std::move(request));
+  renderer_binding_.Bind(std::move(request),
+                         GetRendererScheduler()->IPCTaskRunner());
 }
 
 bool RenderThreadImpl::NeedsToRecordFirstActivePaint(