[WebGPU] Fix DCHECK crash when loadValue="load"

When loadValue is a "load", we make a new GPUColor and convert it to a dawn type. However, the conversion tries to access the rgba components of the color, which triggers checks such as has_r_ (since the color hasn't been set).

Bug: 877147
Change-Id: Iec24f35a94beb0e17d17d4d7c9f7ac5175c949e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1724584
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682210}

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

@@ -36,7 +36,6 @@ DawnRenderPassColorAttachmentDescriptor AsDawnType(
   if (webgpu_desc->loadValue().IsGPULoadOp()) {
     const WTF::String& gpuLoadOp = webgpu_desc->loadValue().GetAsGPULoadOp();
     dawn_desc.loadOp = AsDawnEnum<DawnLoadOp>(gpuLoadOp);
-    dawn_desc.clearColor = AsDawnType(GPUColor::Create());
 
   } else if (webgpu_desc->loadValue().IsGPUColor()) {
     GPUColor* gpuColor = webgpu_desc->loadValue().GetAsGPUColor();