Batch multiple single NVPR draw paths to instanced draws

src/gpu/batches/GrDrawPathBatch.h

Index: src/gpu/batches/GrDrawPathBatch.h
diff --git a/src/gpu/batches/GrDrawPathBatch.h b/src/gpu/batches/GrDrawPathBatch.h
index d29d046de3c9607b452a736dac3d74eb8a79897c..6d5c69a3466fb82c6a43a752c4f343fc890d23c4 100644
--- a/src/gpu/batches/GrDrawPathBatch.h
+++ b/src/gpu/batches/GrDrawPathBatch.h
@@ -76,19 +76,26 @@ private:
     GrDrawPathBatch(const SkMatrix& viewMatrix, GrColor color, GrPathRendering::FillType fill,
                     const GrPath* path)
         : INHERITED(ClassID(), viewMatrix, color, fill)
-        , fPath(path) {
+        , fPath(path)
+        , fNext(nullptr)
+        , fLastSlot(&fNext)
+        , fTotalPathCount(1) {
         fBounds = path->getBounds();
         viewMatrix.mapRect(&fBounds);
+        fPathBounds = fBounds;
     }
-
-    bool onCombineIfPossible(GrBatch* t, const GrCaps& caps) override { return false; }
+    static bool ListBoundsIntersects(const GrDrawPathBatch* a, const GrDrawPathBatch* b);
+    bool onCombineIfPossible(GrBatch* t, const GrCaps& caps) override;
 
     void onPrepare(GrBatchFlushState*) override {}
 
     void onDraw(GrBatchFlushState* state) override;
 
     GrPendingIOResource<const GrPath, kRead_GrIOType> fPath;
-
+    SkRect fPathBounds;
+    sk_sp<GrDrawPathBatch> fNext;       // Batch union is made with a linked list of batch nodes.
+    sk_sp<GrDrawPathBatch>* fLastSlot;  // Points to the fNext of the last batch in the batch list.
+    int fTotalPathCount;
     typedef GrDrawPathBatchBase INHERITED;
 };