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

dm/DMUtil.cpp

Index: dm/DMUtil.cpp
diff --git a/dm/DMUtil.cpp b/dm/DMUtil.cpp
index 19b1c0f397f99e9cee8f75c41a4c0b21e243e95e..a702bbe874953492729164c157b7277cf10a995b 100644
--- a/dm/DMUtil.cpp
+++ b/dm/DMUtil.cpp
@@ -1,11 +1,25 @@
 #include "DMUtil.h"
 
 #include "SkColorPriv.h"
+#include "SkCommandLineFlags.h"
 #include "SkPicture.h"
 #include "SkPictureRecorder.h"
 
+DEFINE_string(matrix, "1 0 0 0 1 0 0 0 1",
+              "Matrix to apply to the canvas before drawing.");
+
 namespace DM {
 
+void CanvasPreflight(SkCanvas* canvas) {
+    if (FLAGS_matrix.count() == 9) {
+        SkMatrix m;
+        for (int i = 0; i < 9; i++) {
+            m[i] = (SkScalar)atof(FLAGS_matrix[i]);
+        }
+        canvas->concat(m);
+    }
+}
+
 SkString UnderJoin(const char* a, const char* b) {
     SkString s;
     s.appendf("%s_%s", a, b);
@@ -27,6 +41,7 @@ SkPicture* RecordPicture(skiagm::GM* gm, SkBBHFactory* factory, bool skr) {
 
     SkCanvas* canvas = skr ? recorder.EXPERIMENTAL_beginRecording(w, h, factory)
                            : recorder.  DEPRECATED_beginRecording(w, h, factory);
+    CanvasPreflight(canvas);
     canvas->concat(gm->getInitialTransform());
     gm->draw(canvas);
     canvas->flush();