Bug 1624768 - Forbid multisampled unsized DEPTH_STENCIL. r=lsalzman

Differential Revision: https://phabricator.services.mozilla.com/D68135

--HG--
extra : moz-landing-system : lando

dom/canvas/ClientWebGLContext.cpp

@@ -3181,6 +3181,14 @@ void ClientWebGLContext::RenderbufferStorageMultisample(GLenum target,
     return;
   }
 
+  if (internalFormat == LOCAL_GL_DEPTH_STENCIL && samples > 0) {
+    // While our backend supports it trivially, the spec forbids it.
+    EnqueueError(LOCAL_GL_INVALID_OPERATION,
+                 "WebGL 1's DEPTH_STENCIL format may not be multisampled. Use "
+                 "DEPTH24_STENCIL8 when `samples > 0`.");
+    return;
+  }
+
   Run<RPROC(RenderbufferStorageMultisample)>(
       rb->mId, static_cast<uint32_t>(samples), internalFormat,
       static_cast<uint32_t>(width), static_cast<uint32_t>(height));