Reland of add a ClassID function to GrBatch (patchset #1 id:1 of https://codereview.chromium.org/1353043002/ )

Reason for revert:
DEPS roll seems to have landed w/o this revert, so revert it again

Original issue's description:
> Revert of add a ClassID function to GrBatch (patchset #5 id:80001 of https://codereview.chromium.org/1352813003/ )
>
> Reason for revert:
> Speculative revert to unblock DEPS roll
>
> Original issue's description:
> > add a ClassID function to GrBatch
> >
> > BUG=skia:
> >
> > Committed: https://skia.googlesource.com/skia/+/4078d529e9e199eea13456db7bf3a63a104ab5b9
> >
> > Committed: https://skia.googlesource.com/skia/+/eb44d53cf96a7eaf103a98d76079ce1f5495e343
>
> TBR=robertphillips@google.com,bsalomon@google.com,joshualitt@google.com,joshualitt@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/48e3a45ade15c52c0c1a10cb00907dd444897745

TBR=robertphillips@google.com,bsalomon@google.com,joshualitt@google.com,joshualitt@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1344373005
diff --git a/gm/convexpolyeffect.cpp b/gm/convexpolyeffect.cpp
index c014e6a..35cc498 100644
--- a/gm/convexpolyeffect.cpp
+++ b/gm/convexpolyeffect.cpp
@@ -31,6 +31,7 @@
 
 class ConvexPolyTestBatch : public GrTestBatch {
 public:
+    DEFINE_BATCH_CLASS_ID
     struct Geometry : public GrTestBatch::Geometry {
         SkRect fBounds;
     };
@@ -43,9 +44,8 @@
 
 private:
     ConvexPolyTestBatch(const GrGeometryProcessor* gp, const Geometry& geo)
-        : INHERITED(gp, geo.fBounds)
+        : INHERITED(ClassID(), gp, geo.fBounds)
         , fGeometry(geo) {
-        this->initClassID<ConvexPolyTestBatch>();
     }
 
     Geometry* geoData(int index) override {