QPainter: replace an QVector with QVarLengthArray

We usually do not keep a lot of QPainter states, but we need to
call 1 allocation and 1 reallocation for keep 4 states. It will be
better to use QVarLengthArray with preallocation for 8 states.

Change-Id: Iacb6aa7a73807491534b1a915453f218d6e4305b
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

src/gui/painting/qpainter_p.h

@@ -51,6 +51,7 @@
 // We mean it.
 //
 
+#include <QtCore/qvarlengtharray.h>
 #include <QtGui/private/qtguiglobal_p.h>
 #include "QtGui/qbrush.h"
 #include "QtGui/qfont.h"
@@ -202,7 +203,7 @@ public:
     QPainterPrivate **d_ptrs;
 
     QPainterState *state;
-    QVector<QPainterState*> states;
+    QVarLengthArray<QPainterState *, 8> states;
 
     mutable QPainterDummyState *dummyState;