[WebGPU] Do not require vertexInput in GPURenderPipelineDescriptor

Following WebGPU spec change at https://github.com/gpuweb/gpuweb/issues/378,
vertexInput descriptor from GPURenderPipelineDescriptor should not be
required anymore.

Bug: 877147
Change-Id: Ifdd0ba7ff6af2b8648ad45d029e5ef7b8484f8a8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1776023
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691978}

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

@@ -229,17 +229,23 @@ GPURenderPipeline* GPURenderPipeline::Create(
     dawn_desc.fragmentStage = nullptr;
   }
 
+  DawnVertexInputInfo vertex_input_info;
+  if (webgpu_desc->hasVertexInput()) {
     // TODO(crbug.com/dawn/131): Update Dawn to match WebGPU vertex input
     v8::Isolate* isolate = script_state->GetIsolate();
-  ExceptionState exception_state(isolate, ExceptionState::kConstructionContext,
+    ExceptionState exception_state(isolate,
+                                   ExceptionState::kConstructionContext,
                                    "GPUVertexInputDescriptor");
-  DawnVertexInputInfo vertex_input_info = GPUVertexInputAsDawnInputState(
+    vertex_input_info = GPUVertexInputAsDawnInputState(
         isolate, webgpu_desc->vertexInput(), exception_state);
     dawn_desc.vertexInput = &std::get<0>(vertex_input_info);
 
     if (exception_state.HadException()) {
       return nullptr;
     }
+  } else {
+    dawn_desc.vertexInput = nullptr;
+  }
 
   dawn_desc.primitiveTopology =
       AsDawnEnum<DawnPrimitiveTopology>(webgpu_desc->primitiveTopology());

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

@@ -12,7 +12,7 @@ dictionary GPURenderPipelineDescriptor : GPUPipelineDescriptorBase {
     GPURasterizationStateDescriptor rasterizationState;
     required sequence<GPUColorStateDescriptor> colorStates;
     GPUDepthStencilStateDescriptor depthStencilState;
-    required GPUVertexInputDescriptor vertexInput;
+    GPUVertexInputDescriptor vertexInput;
 
     unsigned long sampleCount = 1;