message: Reorder backend connections so that explicit APIs come first
  This makes it so that default adapter discovery finds
  Metal/D3D12/Vulkan first.
diff: @@ -101,15 +101,15 @@ namespace dawn_native {
  #if defined(DAWN_ENABLE_BACKEND_METAL)
  Register(metal::Connect(this), BackendType::Metal);
  #endif // defined(DAWN_ENABLE_BACKEND_METAL)
  -#if defined(DAWN_ENABLE_BACKEND_NULL)
  - Register(null::Connect(this), BackendType::Null);
  -#endif // defined(DAWN_ENABLE_BACKEND_NULL)
  -#if defined(DAWN_ENABLE_BACKEND_OPENGL)
  - Register(opengl::Connect(this), BackendType::OpenGL);
  -#endif // defined(DAWN_ENABLE_BACKEND_OPENGL)
  #if defined(DAWN_ENABLE_BACKEND_VULKAN)
  Register(vulkan::Connect(this), BackendType::Vulkan);
  #endif // defined(DAWN_ENABLE_BACKEND_VULKAN)
  +#if defined(DAWN_ENABLE_BACKEND_OPENGL)
  + Register(opengl::Connect(this), BackendType::OpenGL);
  +#endif // defined(DAWN_ENABLE_BACKEND_OPENGL)
  +#if defined(DAWN_ENABLE_BACKEND_NULL)
  + Register(null::Connect(this), BackendType::Null);
  +#endif // defined(DAWN_ENABLE_BACKEND_NULL)
  mBackendsConnected = true;
  }
  