Bug 1774261 part 0: Make nsCSSRendering.cpp include its own header first. r=emilio

This patch does not change behavior.

This change is per our "Foo.cpp should have Foo.h as its first include"
convention, which helps us ensure that the header (nsCSSRendering.h in this
case) has all of the includes/declarations that it needs to compile properly on
its own, and doesn't have a fragile requirement that some other header must
always be included before it.

Differential Revision: https://phabricator.services.mozilla.com/D149336

layout/painting/nsCSSRendering.cpp

@@ -6,6 +6,8 @@
 
 /* utility functions for drawing borders and backgrounds */
 
+#include "nsCSSRendering.h"
+
 #include <ctime>
 
 #include "gfx2DGlue.h"
@@ -41,7 +43,6 @@
 #include "nsIScrollableFrame.h"
 #include "imgIContainer.h"
 #include "ImageOps.h"
-#include "nsCSSRendering.h"
 #include "nsCSSColorUtils.h"
 #include "nsITheme.h"
 #include "nsLayoutUtils.h"