services/ui: Allow injecting the IO thread task runner for gpu channel.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index a6ba224890db29727486a1ada531d87055d337d8..0ac4350be350739fcbc38cbd2439bafa0f43c295 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -637,6 +637,8 @@ void RenderThreadImpl::Init(
   if (IsRunningInMash()) {
     gpu_service_ =
         ui::GpuService::Initialize(GetMojoShellConnection()->GetConnector());
+    gpu_service_->SetIOThreadTaskRunner(
+        ChildProcess::current()->io_task_runner());
   }
 #endif