[Ozone/X11] Use UI message loop for TestGpuServiceHolder

After [1], multiple MessagePumpGlibs may be created, so the workaround
for Ozone/X11 is no longer necessary.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/2343314

BUG=1078392
R=rjkroege
CC=spang

Change-Id: I985c83e21a17e802fe9356c6cbd6c16513487907
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2364796
Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800992}

components/viz/test/test_gpu_service_holder.cc

@@ -148,16 +148,9 @@ TestGpuServiceHolder::TestGpuServiceHolder(
   base::Thread::Options gpu_thread_options;
 #if defined(USE_OZONE)
   if (features::IsUsingOzonePlatform()) {
-    base::MessagePumpType message_pump_type_for_gpu =
-        ui::OzonePlatform::GetInstance()
-            ->GetPlatformProperties()
-            .message_pump_type_for_gpu;
-    // X11 platform uses UI thread for GPU main, but 2 UI threads is
-    // causing crashes in linux-ozone-rel.
-    // TODO(crbug.com/1078392): Investigate and fix.
-    if (message_pump_type_for_gpu != base::MessagePumpType::UI) {
-      gpu_thread_options.message_pump_type = message_pump_type_for_gpu;
-    }
+    gpu_thread_options.message_pump_type = ui::OzonePlatform::GetInstance()
+                                               ->GetPlatformProperties()
+                                               .message_pump_type_for_gpu;
   }
 #endif