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

src/gpu/batches/GrTestBatch.h

Index: src/gpu/batches/GrTestBatch.h
diff --git a/src/gpu/batches/GrTestBatch.h b/src/gpu/batches/GrTestBatch.h
index 68ea676d254722a4903d3e6da1ca3c2a1d28ea58..d8986b681659303c6ebfbd41f06ea49c4a4c70c2 100644
--- a/src/gpu/batches/GrTestBatch.h
+++ b/src/gpu/batches/GrTestBatch.h
@@ -16,7 +16,7 @@
  * A simple batch only for testing purposes which actually doesn't batch at all, but can fit into
  * the batch pipeline and generate arbitrary geometry
  */
-class GrTestBatch : public GrBatch {
+class GrTestBatch : public GrVertexBatch {
 public:
     struct Geometry {
         GrColor fColor;