Complete per-backend AdapterDiscoveryOptions

D3D12, OpenGL, and OpenGLES have their own backend-specific
AdapterDiscoveryOptions. Add the same for Vulkan and Metal so we can
selectively discover just Vulkan or Metal adapters.

The Vulkan options include a boolean forceSwiftShader to force
Dawn to discover only SwiftShader on the Vulkan backend.

Also, refactor D3D12's DiscoverDefaultAdapters to simply call
DiscoverAdapters to match the other backends.

Bug: chromium:1266550
Change-Id: I137f94b40084b2d0ddeda39b6b7ef20f033d8a4b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/69522
Commit-Queue: Austin Eng <enga@chromium.org>
Reviewed-by: Loko Kung <lokokung@google.com>

src/include/dawn_native/D3D12Backend.h

@@ -95,6 +95,7 @@ namespace dawn_native { namespace d3d12 {
     };
 
     struct DAWN_NATIVE_EXPORT AdapterDiscoveryOptions : public AdapterDiscoveryOptionsBase {
+        AdapterDiscoveryOptions();
         AdapterDiscoveryOptions(Microsoft::WRL::ComPtr<IDXGIAdapter> adapter);
 
         Microsoft::WRL::ComPtr<IDXGIAdapter> dxgiAdapter;

src/include/dawn_native/MetalBackend.h

@@ -33,6 +33,11 @@ typedef __IOSurface* IOSurfaceRef;
 #endif  //__OBJC__
 
 namespace dawn_native { namespace metal {
+
+    struct DAWN_NATIVE_EXPORT AdapterDiscoveryOptions : public AdapterDiscoveryOptionsBase {
+        AdapterDiscoveryOptions();
+    };
+
     struct DAWN_NATIVE_EXPORT ExternalImageDescriptorIOSurface : ExternalImageDescriptor {
       public:
         ExternalImageDescriptorIOSurface();
@@ -50,11 +55,14 @@ namespace dawn_native { namespace metal {
     // when they are "scheduled". Submitting other operations before the command buffer is
     // scheduled could lead to races in who gets scheduled first and incorrect rendering.
     DAWN_NATIVE_EXPORT void WaitForCommandsToBeScheduled(WGPUDevice device);
+
 }}  // namespace dawn_native::metal
 
 #ifdef __OBJC__
 namespace dawn_native { namespace metal {
+
     DAWN_NATIVE_EXPORT id<MTLDevice> GetMetalDevice(WGPUDevice device);
+
 }}      // namespace dawn_native::metal
 #endif  // __OBJC__
 

src/include/dawn_native/VulkanBackend.h

@@ -33,6 +33,12 @@ namespace dawn_native { namespace vulkan {
     DAWN_NATIVE_EXPORT WGPUTextureFormat
     GetNativeSwapChainPreferredFormat(const DawnSwapChainImplementation* swapChain);
 
+    struct DAWN_NATIVE_EXPORT AdapterDiscoveryOptions : public AdapterDiscoveryOptionsBase {
+        AdapterDiscoveryOptions();
+
+        bool forceSwiftShader = false;
+    };
+
     struct DAWN_NATIVE_EXPORT ExternalImageDescriptorVk : ExternalImageDescriptor {
       public:
         // The following members may be ignored if |ExternalImageDescriptor::isInitialized| is false