Clean up logic re: virtualized contexts and passthrough

This logic was being duplicated on Mac because of an earlier change.

Bug: chromium:914976
Change-Id: I724c3447f9ed50c54e0e448e994a74f693f05168
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2316150Reviewed-by: Kramer Ge <fangzhoug@chromium.org>
Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Cr-Commit-Position: refs/heads/master@{#791869}

gpu/ipc/in_process_gpu_thread_holder.cc

@@ -91,11 +91,7 @@ void InProcessGpuThreadHolder::InitializeOnGpuThread(
 #if defined(OS_MACOSX)
   // Virtualize GpuPreference:::kLowPower contexts by default on OS X to prevent
   // performance regressions when enabling FCM. https://crbug.com/180463
-  // Do not enable virtualized contexts if the passthrough is enabled, because
-  // ANGLE already uses virtualized contexts.
-  if (!use_passthrough_cmd_decoder) {
-    use_virtualized_gl_context = true;
-  }
+  use_virtualized_gl_context = true;
 #endif
   use_virtualized_gl_context |=
       gpu_driver_bug_workarounds.use_virtualized_gl_contexts;