Unreviewed, reverting 266873@main.

https://bugs.webkit.org/show_bug.cgi?id=260193

This was an incorrect revert

Reverted changeset:

"Unreviewed, reverting 266754@main."
https://bugs.webkit.org/show_bug.cgi?id=260172
https://commits.webkit.org/266873@main

Canonical link: https://commits.webkit.org/266897@main

Source/WTF/wtf/PlatformEnableCocoa.h

@@ -900,6 +900,6 @@
 #define ENABLE_SAMPLE_BUFFER_CONTENT_KEY_SESSION_SUPPORT 1
 #endif
 
-#if !defined(ENABLE_PREWARM_WEBPROCESS_ON_PROVISIONAL_LOAD) && PLATFORM(IOS)
+#if !defined(ENABLE_PREWARM_WEBPROCESS_ON_PROVISIONAL_LOAD) && (PLATFORM(IOS) || PLATFORM(MAC))
 #define ENABLE_PREWARM_WEBPROCESS_ON_PROVISIONAL_LOAD 1
 #endif