[WebGPU] add "readonly-storage-buffer" bind group layout binding type

This CL adds the "readonly-storage-buffer" bind group layout binding
type. When used though, it currently raises a validation error as Dawn
doesn't support it yet.

It also removes the unused `dynamic-uniform-buffer` bind group layout
binding type.

Bug: 877147
Change-Id: I3266b8931fee3e3f66dd170771195374132feaf0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1730911Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: François Beaufort <beaufort.francois@gmail.com>
Cr-Commit-Position: refs/heads/master@{#683146}

third_party/blink/renderer/modules/webgpu/dawn_conversions.cc

@@ -17,18 +17,21 @@ namespace blink {
 
 template <>
 DawnBindingType AsDawnEnum<DawnBindingType>(const WTF::String& webgpu_enum) {
+  if (webgpu_enum == "uniform-buffer") {
+    return DAWN_BINDING_TYPE_UNIFORM_BUFFER;
+  }
+  if (webgpu_enum == "storage-buffer") {
+    return DAWN_BINDING_TYPE_STORAGE_BUFFER;
+  }
+  if (webgpu_enum == "readonly-storage-buffer") {
+    return DAWN_BINDING_TYPE_READONLY_STORAGE_BUFFER;
+  }
   if (webgpu_enum == "sampler") {
     return DAWN_BINDING_TYPE_SAMPLER;
   }
   if (webgpu_enum == "sampled-texture") {
     return DAWN_BINDING_TYPE_SAMPLED_TEXTURE;
   }
-  if (webgpu_enum == "storage-buffer") {
-    return DAWN_BINDING_TYPE_STORAGE_BUFFER;
-  }
-  if (webgpu_enum == "uniform-buffer") {
-    return DAWN_BINDING_TYPE_UNIFORM_BUFFER;
-  }
   NOTREACHED();
   return DAWN_BINDING_TYPE_FORCE32;
 }

third_party/blink/renderer/modules/webgpu/gpu_bind_group_layout_binding.idl

@@ -14,8 +14,8 @@ dictionary GPUBindGroupLayoutBinding {
 
 enum GPUBindingType {
     "uniform-buffer",
-    "dynamic-uniform-buffer",
+    "storage-buffer",
+    "readonly-storage-buffer",
     "sampler",
     "sampled-texture",
-    "storage-buffer",
 };