Implement readonly depth/stencil attachment on Metal

Bug: dawn:485
Change-Id: Ifb119361d8c383c43b4fad51f6a1f6b12ccea434
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/76040
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Yunchao He <yunchao.he@intel.com>
diff --git a/src/tests/end2end/ReadOnlyDepthStencilAttachmentTests.cpp b/src/tests/end2end/ReadOnlyDepthStencilAttachmentTests.cpp
index c31a322..8548a1a 100644
--- a/src/tests/end2end/ReadOnlyDepthStencilAttachmentTests.cpp
+++ b/src/tests/end2end/ReadOnlyDepthStencilAttachmentTests.cpp
@@ -316,10 +316,10 @@
 }
 
 DAWN_INSTANTIATE_TEST_P(ReadOnlyDepthAttachmentTests,
-                        {D3D12Backend(), VulkanBackend()},
+                        {D3D12Backend(), MetalBackend(), VulkanBackend()},
                         std::vector<wgpu::TextureFormat>(utils::kDepthFormats.begin(),
                                                          utils::kDepthFormats.end()));
 DAWN_INSTANTIATE_TEST_P(ReadOnlyStencilAttachmentTests,
-                        {D3D12Backend(), VulkanBackend()},
+                        {D3D12Backend(), MetalBackend(), VulkanBackend()},
                         std::vector<wgpu::TextureFormat>(utils::kStencilFormats.begin(),
                                                          utils::kStencilFormats.end()));