Bug 1940800: Spoof hardware support in RFP. r=tjr

Differential Revision: https://phabricator.services.mozilla.com/D233755

dom/webgpu/Adapter.cpp

@@ -298,6 +298,13 @@ const RefPtr<SupportedLimits>& Adapter::Limits() const { return mLimits; }
 const RefPtr<AdapterInfo>& Adapter::Info() const { return mInfo; }
 
 bool Adapter::IsFallbackAdapter() const {
+  if (GetParentObject()->ShouldResistFingerprinting(
+          RFPTarget::WebGPUIsFallbackAdapter)) {
+    // Always report hardware support for WebGPU.
+    // This behaviour matches with media capabilities API.
+    return false;
+  }
+
   return mInfoInner->device_type == ffi::WGPUDeviceType::WGPUDeviceType_Cpu;
 }
 

toolkit/components/resistfingerprinting/RFPTargets.inc

@@ -95,6 +95,7 @@ ITEM_VALUE(SiteSpecificZoom,            61)
 ITEM_VALUE(FontVisibilityRestrictGenerics, 62)
 ITEM_VALUE(WebVTT,                      63)
 ITEM_VALUE(WebGPULimits,                64)
+ITEM_VALUE(WebGPUIsFallbackAdapter,     65)
 
 // !!! Don't forget to update kDefaultFingerprintingProtections in nsRFPService.cpp
 // if necessary.