Bug 1716045 - Optimize ArcSlice equality operator for pointer equalit…

…y. r=jfkthame

Just drive-by, but seems reasonable to avoid the per-element comparison
if the pointers are the same.

Depends on D118015

Differential Revision: https://phabricator.services.mozilla.com/D118016

layout/style/ServoStyleConstsInlines.h

@@ -225,7 +225,7 @@ inline Span<const T> StyleArcSlice<T>::AsSpan() const {
 template <typename T>
 inline bool StyleArcSlice<T>::operator==(const StyleArcSlice& aOther) const {
   ASSERT_CANARY
-  return AsSpan() == aOther.AsSpan();
+  return _0.ptr == aOther._0.ptr || AsSpan() == aOther.AsSpan();
 }
 
 template <typename T>