[WebGPU] Make GPUTextureDescriptor.size required

WebGPU spec says GPUTextureDescriptor.size is required when creating
a texture.

Bug: 877147
Change-Id: Ie0f68f7dd54c55b6d4aab826dc52274af386b54e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1724090
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: François Beaufort <beaufort.francois@gmail.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681754}

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

@@ -5,7 +5,7 @@
 // https://github.com/gpuweb/gpuweb/blob/master/design/sketch.webidl
 
 dictionary GPUTextureDescriptor {
-    GPUExtent3D size;
+    required GPUExtent3D size;
     unsigned long arrayLayerCount = 1;
     unsigned long mipLevelCount = 1;
     unsigned long sampleCount = 1;