DM: make GPU tasks multithreaded again. Big refactor.

dm/DMTileGridTask.cpp

 #include "DMTileGridTask.h"
 #include "DMWriteTask.h"
 #include "DMUtil.h"
 
 #include "SkCommandLineFlags.h"
 #include "SkPicture.h"
 #include "SkTileGridPicture.h"
 
 // TODO(mtklein): Tile grid tests are currently failing.  (Skia issue 1198).  When fixed, -> true.
 DEFINE_bool(tileGrid, false, "If true, run picture replay tests with a tile grid.");
 
 namespace DM {
 
 TileGridTask::TileGridTask(const Task& parent, skiagm::GM* gm, SkBitmap reference, SkISize tileSize)
-    : Task(parent)
+    : CpuTask(parent)
     , fName(UnderJoin(parent.name().c_str(), "tilegrid"))
     , fGM(gm)
     , fReference(reference)
     , fTileSize(tileSize)
     {}
 
 static int tiles_needed(int fullDimension, int tileDimension) {
     return (fullDimension + tileDimension - 1) / tileDimension;
 }
 
@@ skipping 45 matching lines @@
     if (fGM->getFlags() & skiagm::GM::kSkipPicture_Flag) {
         return true;
     }
     if (fGM->getFlags() & skiagm::GM::kSkipTiled_Flag) {
         return true;
     }
     return !FLAGS_tileGrid;
 }
 
 }  // namespace DM