Fix missing include for std::unique_ptr in D3D12Binding.cpp

Bug: dawn:99
Change-Id: Ifeaa69b3061fe962a39f0b13bdee028dbeb2677d
Reviewed-on: https://dawn-review.googlesource.com/c/4320
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/utils/D3D12Binding.cpp

@@ -21,6 +21,8 @@
 #define GLFW_EXPOSE_NATIVE_WIN32
 #include "GLFW/glfw3native.h"
 
+#include <memory>
+
 namespace utils {
 
     class D3D12Binding : public BackendBinding {