Vulkan: Support feature chromium_experimental_dp4a

This patch adds the support of the experimental feature
chromium_experimental_dp4a on Vulkan. Currently this
feature is enabled on Vulkan backend only when DP4a
instructions are hardware-accelerated.

Bug: tint:1497
Test: dawn_end2end_tests
Change-Id: I5a63111a6b5972aa1934f0e7be984ebdb1e35080
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/91520
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/dawn/native/Device.cpp

@@ -201,8 +201,6 @@ DeviceBase::DeviceBase(AdapterBase* adapter, const DeviceDescriptor* descriptor)
 
     mFormatTable = BuildFormatTable(this);
 
-    SetWGSLExtensionAllowList();
-
     if (descriptor->label != nullptr && strlen(descriptor->label) != 0) {
         mLabel = descriptor->label;
     }
@@ -229,6 +227,8 @@ DeviceBase::~DeviceBase() {
 }
 
 MaybeError DeviceBase::Initialize(Ref<QueueBase> defaultQueue) {
+    SetWGSLExtensionAllowList();
+
     mQueue = std::move(defaultQueue);
 
 #if defined(DAWN_ENABLE_ASSERTS)
@@ -1284,16 +1284,7 @@ void DeviceBase::ApplyFeatures(const DeviceDescriptor* deviceDescriptor) {
 }
 
 bool DeviceBase::IsFeatureEnabled(Feature feature) const {
-    if (mEnabledFeatures.IsEnabled(feature)) {
-        // Currently we can only use DXC to compile HLSL shaders using float16, and
-        // ChromiumExperimentalDp4a is an experimental feature which can only be enabled with toggle
-        // "use_dxc".
-        if (feature == Feature::ChromiumExperimentalDp4a || feature == Feature::ShaderFloat16) {
-            return IsToggleEnabled(Toggle::UseDXC);
-        }
-        return true;
-    }
-    return false;
+    return mEnabledFeatures.IsEnabled(feature);
 }
 
 void DeviceBase::SetWGSLExtensionAllowList() {