add a ClassID function to GrBatch

src/gpu/batches/GrDiscardBatch.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrDiscardBatch_DEFINED
 #define GrDiscardBatch_DEFINED
 
 #include "GrBatch.h"
 #include "GrBatchFlushState.h"
 #include "GrGpu.h"
 #include "GrRenderTarget.h"
 
 class GrDiscardBatch final : public GrBatch {
 public:
+    DEFINE_BATCH_CLASS_ID
+
     GrDiscardBatch(GrRenderTarget* rt)
-        : fRenderTarget(rt) {
-        this->initClassID<GrDiscardBatch>();
+        : INHERITED(ClassID())
+        , fRenderTarget(rt) {
         fBounds = SkRect::MakeWH(SkIntToScalar(rt->width()), SkIntToScalar(rt->height()));
     }
 
     const char* name() const override { return "Discard"; }
 
     uint32_t renderTargetUniqueID() const override { return fRenderTarget.get()->getUniqueID(); }
 
     SkString dumpInfo() const override {
         SkString string;
         string.printf("RT: 0x%p", fRenderTarget.get());
         return string;
     }
 
 private:
     bool onCombineIfPossible(GrBatch* that, const GrCaps& caps) override {
         return fRenderTarget == that->cast<GrDiscardBatch>()->fRenderTarget;
     }
 
     void onPrepare(GrBatchFlushState*) override {}
 
     void onDraw(GrBatchFlushState* state) override {
         state->gpu()->discard(fRenderTarget.get());
     }
 
     GrPendingIOResource<GrRenderTarget, kWrite_GrIOType> fRenderTarget;
+
+    typedef GrBatch INHERITED;
 };
 
 #endif