Add option to skip rects to drawImageLattice()

HWUI skips transparent rects when drawing.

When skia draws using bilerp, we will blend
transparent rects with neighboring rects and might
draw a bit of a smudge.

This CL adds the option to skip rects, allowing us
to have compatible behavior with the framework.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2305433002

Review-Url: https://codereview.chromium.org/2305433002
diff --git a/src/core/SkRecordDraw.cpp b/src/core/SkRecordDraw.cpp
index 6545586..2952591 100644
--- a/src/core/SkRecordDraw.cpp
+++ b/src/core/SkRecordDraw.cpp
@@ -106,6 +106,7 @@
     lattice.fXDivs = r.xDivs;
     lattice.fYCount = r.yCount;
     lattice.fYDivs = r.yDivs;
+    lattice.fFlags = (0 == r.flagCount) ? nullptr : r.flags;
     fCanvas->drawImageLattice(r.image.get(), lattice, r.dst, r.paint);
 }