Optimize the QMatrix4x4 after a conversion from SkMatrix44

This avoids using a General matrix for tile transformations which are
usually only translations in our case.

Change-Id: Ic947d7ef9b78de6d5d16ea718cc03255e38a8097
Reviewed-by: Michael Bruning <michael.bruning@digia.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>

src/core/type_conversion.h

@@ -121,11 +121,13 @@ inline QColor toQt(const SkColor &c)
 
 inline QMatrix4x4 toQt(const SkMatrix44 &m)
 {
-    return QMatrix4x4(
+    QMatrix4x4 qtMatrix(
         m.get(0, 0), m.get(0, 1), m.get(0, 2), m.get(0, 3),
         m.get(1, 0), m.get(1, 1), m.get(1, 2), m.get(1, 3),
         m.get(2, 0), m.get(2, 1), m.get(2, 2), m.get(2, 3),
         m.get(3, 0), m.get(3, 1), m.get(3, 2), m.get(3, 3));
+    qtMatrix.optimize();
+    return qtMatrix;
 }
 
 inline QDateTime toQt(base::Time time)