Experiment: add flag for finish-recording to return null

tests/RecordReplaceDrawTest.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
 
 #if SK_SUPPORT_GPU
@@ skipping 60 matching lines @@
     sk_sp<SkPicture> pic;
 
     {
         SkPictureRecorder recorder;
         SkCanvas* canvas = recorder.beginRecording(SkIntToScalar(kWidth), SkIntToScalar(kHeight));
 
         // We won't balance this, but GrRecordReplaceDraw will for us.
         canvas->save();
         canvas->scale(2, 2);
         pic = recorder.finishRecordingAsPicture();
+
+        // we may have optimized everything away. If so, just return
+        if (pic->approximateOpCount() == 0) {
+            return;
+        }
     }
 
     SkRecord rerecord;
     SkRecorder canvas(&rerecord, kWidth, kHeight);
 
     GrRecordReplaceDraw(pic.get(), &canvas, nullptr, SkMatrix::I(), nullptr/*callback*/);
 
     // ensure rerecord is balanced (in this case by checking that the count is odd)
     REPORTER_ASSERT(r, (rerecord.count() & 1) == 1);
 }
@@ skipping 54 matching lines @@
         REPORTER_ASSERT(r, 1 == numLayers);
     }
 }
 
 DEF_GPUTEST_FOR_RENDERING_CONTEXTS(RecordReplaceDraw, r, ctxInfo) {
     test_replacements(r, ctxInfo.grContext(), true);
     test_replacements(r, ctxInfo.grContext(), false);
 }
 
 #endif