Start using GrGpuCommandBuffer in GrDrawTarget.

src/gpu/batches/GrDiscardBatch.h

Index: src/gpu/batches/GrDiscardBatch.h
diff --git a/src/gpu/batches/GrDiscardBatch.h b/src/gpu/batches/GrDiscardBatch.h
index 65b6c4bf7d3ab850f0cb5cf0ce46a4088bfeb369..3c19b682465797ad75babf65d5aa2b3fadbda0a6 100644
--- a/src/gpu/batches/GrDiscardBatch.h
+++ b/src/gpu/batches/GrDiscardBatch.h
@@ -42,7 +42,7 @@ private:
     void onPrepare(GrBatchFlushState*) override {}
 
     void onDraw(GrBatchFlushState* state) override {
-        state->gpu()->discard(fRenderTarget.get());
+        state->commandBuffer()->discard(fRenderTarget.get());
     }
 
     GrPendingIOResource<GrRenderTarget, kWrite_GrIOType> fRenderTarget;