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

dm/DMGpuGMTask.cpp

 #include "DMGpuGMTask.h"
-
 #include "DMUtil.h"
 #include "DMWriteTask.h"
 #include "SkCommandLineFlags.h"
 #include "SkSurface.h"
 #include "SkTLS.h"
 
 namespace DM {
 
 GpuGMTask::GpuGMTask(const char* config,
                      Reporter* reporter,
@@ skipping 15 matching lines @@
                                          SkScalarCeilToInt(fGM->height()),
                                          kN32_SkColorType,
                                          kPremul_SkAlphaType);
     SkAutoTUnref<SkSurface> surface(NewGpuSurface(grFactory, fContextType, fGpuAPI, info,
                                                   fSampleCount));
     if (!surface) {
         this->fail("Could not create context for the config and the api.");
         return;
     }
     SkCanvas* canvas = surface->getCanvas();
+    CanvasPreflight(canvas);
 
     canvas->concat(fGM->getInitialTransform());
     fGM->draw(canvas);
     canvas->flush();
 
     SkBitmap bitmap;
     bitmap.setInfo(info);
     canvas->readPixels(&bitmap, 0, 0);
 
     this->spawnChild(SkNEW_ARGS(WriteTask, (*this, "GM", bitmap)));
 }
 
 bool GpuGMTask::shouldSkip() const {
     return kGPUDisabled || SkToBool(fGM->getFlags() & skiagm::GM::kSkipGPU_Flag);
 }
 
 }  // namespace DM