Introduce GrBatch subclasses GrDrawBatch and GrVertexBatch to prepare for non-drawing batches

src/gpu/GrImmediateDrawTarget.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrImmediateDrawTarget.h"
 
 #include "GrGpu.h"
 #include "GrPipeline.h"
 #include "GrRenderTarget.h"
 #include "SkRect.h"
 #include "SkTypes.h"
 
 #include "batches/GrBatch.h"
 
 GrImmediateDrawTarget::GrImmediateDrawTarget(GrContext* context)
     : INHERITED(context)
     , fBatchTarget(this->getGpu())
     , fDrawID(0) {
 }
 
 GrImmediateDrawTarget::~GrImmediateDrawTarget() {
     this->reset();
 }
 
-void GrImmediateDrawTarget::onDrawBatch(GrBatch* batch) {
+void GrImmediateDrawTarget::onDrawBatch(GrDrawBatch* batch) {
     fBatchTarget.resetNumberOfDraws();
 
-    batch->generateGeometry(&fBatchTarget);
-    batch->setNumberOfDraws(fBatchTarget.numberOfDraws());
+    // TODO: encapsulate the specialization of GrVertexBatch in GrVertexBatch so that we can
+    // remove this cast. Currently all GrDrawBatches are in fact GrVertexBatch.
+    GrVertexBatch* vertexBatch = static_cast<GrVertexBatch*>(batch);
+    vertexBatch->generateGeometry(&fBatchTarget);
+    vertexBatch->setNumberOfDraws(fBatchTarget.numberOfDraws());
 
     fBatchTarget.preFlush();
-    fBatchTarget.flushNext(batch->numberOfDraws());
+    fBatchTarget.flushNext(vertexBatch->numberOfDraws());
     fBatchTarget.postFlush();
 }
 
 void GrImmediateDrawTarget::onClear(const SkIRect& rect, GrColor color,
                                     GrRenderTarget* renderTarget) {
     this->getGpu()->clear(rect, color, renderTarget);
 }
 
 void GrImmediateDrawTarget::onCopySurface(GrSurface* dst,
                                           GrSurface* src,
@@ skipping 16 matching lines @@
     this->getGpu()->discard(renderTarget);
 }
 
 void GrImmediateDrawTarget::onReset() {
     fBatchTarget.reset();
 }
 
 void GrImmediateDrawTarget::onFlush() {
     ++fDrawID;
 }