Construct VertexAttributeDescriptor, in order to match web idl

The parameters about vertex attribute were encapsulated in
VertexAttributeDescriptor in web idl. This change construct
this descriptor accordingly.

BUG=dawn:107

Change-Id: Ia1c6e53af951d8f2a0c0b69bdca09291c2661e50
Reviewed-on: https://dawn-review.googlesource.com/c/4620
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Yunchao He <yunchao.he@intel.com>
diff --git a/src/dawn_native/d3d12/InputStateD3D12.cpp b/src/dawn_native/d3d12/InputStateD3D12.cpp
index 3469f9e..9178423 100644
--- a/src/dawn_native/d3d12/InputStateD3D12.cpp
+++ b/src/dawn_native/d3d12/InputStateD3D12.cpp
@@ -78,9 +78,9 @@
             inputElementDescriptor.SemanticName = "TEXCOORD";
             inputElementDescriptor.SemanticIndex = static_cast<uint32_t>(i);
             inputElementDescriptor.Format = VertexFormatType(attribute.format);
-            inputElementDescriptor.InputSlot = attribute.bindingSlot;
+            inputElementDescriptor.InputSlot = attribute.inputSlot;
 
-            const InputInfo& input = GetInput(attribute.bindingSlot);
+            const InputInfo& input = GetInput(attribute.inputSlot);
 
             inputElementDescriptor.AlignedByteOffset = attribute.offset;
             inputElementDescriptor.InputSlotClass = InputStepModeFunction(input.stepMode);