Quit the second GPU process when its job to gather the DX12/Vulkan info is complete.

The previous checkin for "996594:Adding SupportsDX12 and SupportsVulkan to UMA histogram
for the Windows platform" did not quit the GPU process after the job is complete.

base::RunLoop().QuitCurrentWhenIdleDeprecated() is added to the end of the function of the second
GPU process to fix this issue.

BUG=832596
TEST=manual,Chrome task manager
R=zmo@chromium.org

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel
Change-Id: Ifadb24d39b24a9a5a6cdc0c33e66bcfc42d5a5a7
Reviewed-on: https://chromium-review.googlesource.com/1012595Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Maggie Chen <magchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550751}

components/viz/service/gl/gpu_service_impl.cc

@@ -452,6 +452,11 @@ void GpuServiceImpl::GetGpuSupportedRuntimeVersion() {
   DCHECK(command_line->HasSwitch("disable-gpu-sandbox") || in_host_process());
 
   gpu::RecordGpuSupportedRuntimeVersionHistograms(&gpu_info_);
+  if (!in_host_process()) {
+    // The unsandboxed GPU process fulfilled its duty. Rest
+    // in peace.
+    base::RunLoop().QuitCurrentWhenIdleDeprecated();
+  }
 #endif
 }