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

dm/DMPipeTask.cpp

 #include "DMPipeTask.h"
 #include "DMUtil.h"
 #include "DMWriteTask.h"
 
 #include "SamplePipeControllers.h"
 #include "SkCommandLineFlags.h"
 #include "SkGPipe.h"
 
 DEFINE_bool(pipe, true, "If true, check several pipe variants against the reference bitmap.");
 
@@ skipping 37 matching lines @@
     AllocatePixels(fReference, &bitmap);
 
     SkCanvas canvas(bitmap);
     PipeController pipeController(&canvas, &SkImageDecoder::DecodeMemory);
     SkGPipeWriter writer;
 
     SkCanvas* pipeCanvas = writer.startRecording(&pipeController,
                                                  fFlags,
                                                  bitmap.width(),
                                                  bitmap.height());
+    CanvasPreflight(pipeCanvas);
     pipeCanvas->concat(fGM->getInitialTransform());
     fGM->draw(pipeCanvas);
     writer.endRecording();
 
     if (!BitmapsEqual(bitmap, fReference)) {
         this->fail();
         this->spawnChild(SkNEW_ARGS(WriteTask, (*this, "GM", bitmap)));
     }
 }
 
 bool PipeTask::shouldSkip() const {
     if (!FLAGS_pipe) {
         return true;
     }
     if (fGM->getFlags() & skiagm::GM::kSkipPipe_Flag) {
         return true;
     }
     if (fFlags == SkGPipeWriter::kCrossProcess_Flag &&
         fGM->getFlags() & skiagm::GM::kSkipPipeCrossProcess_Flag) {
         return true;
     }
     return false;
 }
 
 }  // namespace DM