Make classes and structures in core/paint fast-allocated.

Source/core/paint/PartPainter.h

Index: Source/core/paint/PartPainter.h
diff --git a/Source/core/paint/PartPainter.h b/Source/core/paint/PartPainter.h
index c1276c20ae330c64b111acc8783bd2cf43316a21..12f0699b494e02bedcfccd82a7562b932c00a203 100644
--- a/Source/core/paint/PartPainter.h
+++ b/Source/core/paint/PartPainter.h
@@ -5,6 +5,8 @@
 #ifndef PartPainter_h
 #define PartPainter_h
 
+#include "wtf/Allocator.h"
+
 namespace blink {
 
 struct PaintInfo;
@@ -12,6 +14,7 @@ class LayoutPoint;
 class LayoutPart;
 
 class PartPainter {
+    STACK_ALLOCATED();
 public:
     PartPainter(LayoutPart& layoutPart) : m_layoutPart(layoutPart) { }