message: Fix compilation on iOS where setDisplaySyncEnabled isn't available.
diff: @@ -84,9 +84,11 @@ namespace dawn_native { namespace metal {
  [mLayer setDevice:ToBackend(GetDevice())->GetMTLDevice()];
  [mLayer setPixelFormat:MetalPixelFormat(GetFormat())];
  - if (@available(macos 10.13, ios 11.0, *)) {
  +#if defined(DAWN_PLATFORM_MACOS)
  + if (@available(macos 10.13, *)) {
  [mLayer setDisplaySyncEnabled:(GetPresentMode() != wgpu::PresentMode::Immediate)];
  }
  +#endif // defined(DAWN_PLATFORM_MACOS)
  // There is no way to control Fifo vs. Mailbox in Metal.
  }
  