Bug 1758156 - Check that the webgpu pref is enabled when creating PWe…

…bGPUParent. r=aosmond

A better solution would check against the same value as reported by gfxConfig, which takes the pref as well as whether webgpu was blocked (for example due to buggy drivers) into account, but this still is good sanity check and easy to uplift.

Differential Revision: https://phabricator.services.mozilla.com/D140535

gfx/ipc/CanvasManagerParent.cpp

@@ -90,6 +90,10 @@ already_AddRefed<dom::PWebGLParent> CanvasManagerParent::AllocPWebGLParent() {
 
 already_AddRefed<webgpu::PWebGPUParent>
 CanvasManagerParent::AllocPWebGPUParent() {
+  if (!StaticPrefs::dom_webgpu_enabled()) {
+    return nullptr;
+  }
+
   return MakeAndAddRef<webgpu::WebGPUParent>();
 }