WebGPU: Always pick the discrete GPU if it is available

This will be replaced when we implement the GPUAdapterOptions
to select high/low power.

Bug: chromium:852089
Change-Id: If698c1edd3c1cb8f6d10377133f276351d05dc2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1572533Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652202}

gpu/command_buffer/service/webgpu_decoder_impl.cc

@@ -371,12 +371,42 @@ ContextResult WebGPUDecoderImpl::Initialize() {
 DawnDevice WebGPUDecoderImpl::CreateDefaultDevice() {
   dawn_instance_->DiscoverDefaultAdapters();
   std::vector<dawn_native::Adapter> adapters = dawn_instance_->GetAdapters();
+
+  dawn_native::Adapter integrated_gpu_adapter = {};
+  dawn_native::Adapter cpu_adapter = {};
+  dawn_native::Adapter unknown_adapter = {};
+
   for (dawn_native::Adapter adapter : adapters) {
     if (adapter.GetBackendType() != dawn_native::BackendType::Null &&
         adapter.GetBackendType() != dawn_native::BackendType::OpenGL) {
-      return adapter.CreateDevice();
+      switch (adapter.GetDeviceType()) {
+        case dawn_native::DeviceType::DiscreteGPU:
+          // For now, we always prefer the discrete GPU
+          return adapter.CreateDevice();
+        case dawn_native::DeviceType::IntegratedGPU:
+          integrated_gpu_adapter = adapter;
+          break;
+        case dawn_native::DeviceType::CPU:
+          cpu_adapter = adapter;
+          break;
+        case dawn_native::DeviceType::Unknown:
+          unknown_adapter = adapter;
+          break;
+        default:
+          NOTREACHED();
+          break;
+      }
     }
   }
+  if (integrated_gpu_adapter) {
+    return integrated_gpu_adapter.CreateDevice();
+  }
+  if (cpu_adapter) {
+    return cpu_adapter.CreateDevice();
+  }
+  if (unknown_adapter) {
+    return unknown_adapter.CreateDevice();
+  }
   return nullptr;
 }