SkRecordDraw: skip draw ops when the clip is empty

dm/DMRecordTask.cpp

 #include "DMRecordTask.h"
 #include "DMUtil.h"
 #include "DMWriteTask.h"
 #include "SkCommandLineFlags.h"
 #include "SkRecordDraw.h"
 #include "SkRecorder.h"
 
 DEFINE_bool(skr, false, "If true, run SKR tests.");
 
 namespace DM {
 
 RecordTask::RecordTask(const Task& parent, skiagm::GM* gm, SkBitmap reference)
     : CpuTask(parent)
     , fName(UnderJoin(parent.name().c_str(), "skr"))
     , fGM(gm)
     , fReference(reference)
     {}
 
 void RecordTask::draw() {
     // Record the GM into an SkRecord.
     SkRecord record;
-    SkRecorder canvas(&record, fReference.width(), fReference.height());
+    SkRecorder canvas(SkRecorder::kWriteOnly_Mode, &record,
+                      fReference.width(), fReference.height());
     canvas.concat(fGM->getInitialTransform());
     fGM->draw(&canvas);
 
     // Draw the SkRecord back into a bitmap.
     SkBitmap bitmap;
     SetupBitmap(fReference.colorType(), fGM.get(), &bitmap);
     SkCanvas target(bitmap);
 
     SkRecordDraw(record, &target);
 
     if (!BitmapsEqual(bitmap, fReference)) {
         this->fail();
         this->spawnChild(SkNEW_ARGS(WriteTask, (*this, bitmap)));
     }
 }
 
 bool RecordTask::shouldSkip() const {
     return !FLAGS_skr;
 }
 
 }  // namespace DM