WebGPU: add shader_float16 extension

This patch exposes the shader_shader16 extension, which allows use
of 16-bit floating-point types in shaders for arithmetic operations
and use of 16-bit types in buffers.

Bug: 996713
Change-Id: Ib09301fb9d396a85926952f9df396f426b15ee1b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2324318
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804020}

gpu/command_buffer/service/webgpu_decoder_impl.cc

@@ -648,6 +648,9 @@ error::Error WebGPUDecoderImpl::InitDawnDeviceAndSetWireServer(
   if (request_device_properties.textureCompressionBC) {
     device_descriptor.requiredExtensions.push_back("texture_compression_bc");
   }
+  if (request_device_properties.shaderFloat16) {
+    device_descriptor.requiredExtensions.push_back("shader_float16");
+  }
 
   WGPUDevice wgpu_device =
       dawn_adapters_[requested_adapter_index].CreateDevice(&device_descriptor);

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

@@ -28,6 +28,8 @@ WGPUDeviceProperties AsDawnType(const GPUDeviceDescriptor* descriptor) {
   requested_device_properties.textureCompressionBC =
       extension_set.Contains("texture-compression-bc") ||
       extension_set.Contains("textureCompressionBC");
+  requested_device_properties.shaderFloat16 =
+      extension_set.Contains("shader-float16");
 
   return requested_device_properties;
 }
@@ -76,6 +78,9 @@ void GPUAdapter::InitializeExtensionNameList() {
     extension_name_list_.emplace_back("texture-compression-bc");
     extension_name_list_.emplace_back("textureCompressionBC");
   }
+  if (adapter_properties_.shaderFloat16) {
+    extension_name_list_.emplace_back("shader-float16");
+  }
 }
 
 ScriptPromise GPUAdapter::requestDevice(ScriptState* script_state,

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

@@ -7,7 +7,8 @@
 enum GPUExtensionName {
     "texture-compression-bc",
     // Non-standard extension name string. Remove after a transition period.
-    "textureCompressionBC"
+    "textureCompressionBC",
+    "shader-float16"
 };
 
 [