dawn: add dawn::Platform hook for querying feature flags

And use it to query "WebGPUUseDXC". This is important because the moment
the feature flag is queried in Chrome is when the user is made part of
the study. Since we normally want only users using WebGPU to be in the
study, we need this query to happen from within Dawn.

Bug: chromium:1474897
Change-Id: I2adad2b3a256fad5c51080b80b348c0ffd5a914d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/153181
Kokoro: Kokoro <[email protected]>
Commit-Queue: Antonio Maiorano <[email protected]>
Reviewed-by: Corentin Wallez <[email protected]>

Author: amaiorano

include/dawn/platform/DawnPlatform.h

@@ -73,6 +73,12 @@ class DAWN_PLATFORM_EXPORT WorkerTaskPool {
                                                           void* userdata) = 0;
 };
 
+// These features map to similarly named ones in src/chromium/src/gpu/config/gpu_finch_features.h
+// in `namespace features`.
+enum class Features {
+    kWebGPUUseDXC,
+};
+
 class DAWN_PLATFORM_EXPORT Platform {
   public:
     Platform();
@@ -123,6 +129,9 @@ class DAWN_PLATFORM_EXPORT Platform {
 
     virtual std::unique_ptr<WorkerTaskPool> CreateWorkerTaskPool();
 
+    // Hook for querying if a Finch feature is enabled.
+    virtual bool IsFeatureEnabled(Features feature);
+
   private:
     Platform(const Platform&) = delete;
     Platform& operator=(const Platform&) = delete;

src/dawn/native/d3d12/PhysicalDeviceD3D12.cpp

@@ -26,6 +26,7 @@
 #include "dawn/native/d3d12/DeviceD3D12.h"
 #include "dawn/native/d3d12/PlatformFunctionsD3D12.h"
 #include "dawn/native/d3d12/UtilsD3D12.h"
+#include "dawn/platform/DawnPlatform.h"
 
 namespace dawn::native::d3d12 {
 
@@ -489,7 +490,10 @@ void PhysicalDevice::SetupBackendAdapterToggles(TogglesState* adapterToggles) co
     if (GetDeviceInfo().shaderModel <= 60) {
         adapterToggles->ForceSet(Toggle::UseDXC, false);
     }
-    adapterToggles->Default(Toggle::UseDXC, true);
+
+    bool useDxc =
+        GetInstance()->GetPlatform()->IsFeatureEnabled(dawn::platform::Features::kWebGPUUseDXC);
+    adapterToggles->Default(Toggle::UseDXC, useDxc);
 #else
     // Default to using FXC
     if (!GetBackend()->IsDXCAvailable()) {

src/dawn/platform/DawnPlatform.cpp

@@ -79,4 +79,16 @@ std::unique_ptr<dawn::platform::WorkerTaskPool> Platform::CreateWorkerTaskPool()
     return std::make_unique<AsyncWorkerThreadPool>();
 }
 
+bool Platform::IsFeatureEnabled(Features feature) {
+    switch (feature) {
+        case Features::kWebGPUUseDXC:
+#ifdef DAWN_USE_BUILT_DXC
+            return true;
+#else
+            return false;
+#endif
+    }
+    return false;
+}
+
 }  // namespace dawn::platform