Add --matrix to DM, to play around with and maybe use on a bot.

dm/DMUtil.h

Index: dm/DMUtil.h
diff --git a/dm/DMUtil.h b/dm/DMUtil.h
index fa29c767570263ceeb58642cafdce41c1fc657fe..49da857edbc1af674f5bc1ead2f559fb14fc1dfc 100644
--- a/dm/DMUtil.h
+++ b/dm/DMUtil.h
@@ -2,6 +2,7 @@
 #define DMUtil_DEFINED
 
 #include "SkBitmap.h"
+#include "SkCanvas.h"
 #include "SkString.h"
 #include "gm.h"
 
@@ -36,6 +37,9 @@ unsigned MaxComponentDifference(const SkBitmap& a, const SkBitmap& b);
 // Are these identical bitmaps?
 bool BitmapsEqual(const SkBitmap& a, const SkBitmap& b);
 
+// Hook to modify canvas using global flag values (e.g. --matrix).
+void CanvasPreflight(SkCanvas*);
+
 }  // namespace DM
 
 #endif  // DMUtil_DEFINED