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

dm/DMPDFTask.cpp

Index: dm/DMPDFTask.cpp
diff --git a/dm/DMPDFTask.cpp b/dm/DMPDFTask.cpp
index c996aae53cfc67c54617be00de3a19d9495b3fed..3102478c2fe5af2fb92bd568da1fed0bb413c284 100644
--- a/dm/DMPDFTask.cpp
+++ b/dm/DMPDFTask.cpp
@@ -71,12 +71,14 @@ void PDFTask::draw() {
     if (fGM.get()) {
         rasterize = 0 == (fGM->getFlags() & skiagm::GM::kSkipPDFRasterization_Flag);
         SinglePagePDF pdf(fGM->width(), fGM->height());
+        CanvasPreflight(pdf.canvas());
         //TODO(mtklein): GM doesn't do this.  Why not?
         //pdf.canvas()->concat(fGM->getInitialTransform());
         fGM->draw(pdf.canvas());
         pdfData.reset(pdf.end());
     } else {
         SinglePagePDF pdf(fPicture->cullRect().width(), fPicture->cullRect().height());
+        CanvasPreflight(pdf.canvas());
         fPicture->playback(pdf.canvas());
         pdfData.reset(pdf.end());
     }