Fix CodecSubset benches seg faults for kIndex8

bench/subset/SubsetZoomBench.cpp

Index: bench/subset/SubsetZoomBench.cpp
diff --git a/bench/subset/SubsetZoomBench.cpp b/bench/subset/SubsetZoomBench.cpp
index 3ce193b6ea8da33e7083da2c1e3386ea58ac2114..39f234a050d8f226b754cf796c193ade08e213d2 100644
--- a/bench/subset/SubsetZoomBench.cpp
+++ b/bench/subset/SubsetZoomBench.cpp
@@ -77,7 +77,8 @@ void SubsetZoomBench::onDraw(const int n, SkCanvas* canvas) {
                 // Note that if we subsetted and scaled in a single step, we could use the
                 // same bitmap - as is often done in actual use cases.
                 SkBitmap bitmap;
-                bitmap.allocPixels(info.makeWH(subsetWidth, subsetHeight));
+                SkImageInfo subsetInfo = info.makeWH(subsetWidth, subsetHeight);
+                alloc_pixels(&bitmap, subsetInfo, colors, colorCount);
 
                 uint32_t bpp = info.bytesPerPixel();
                 scanlineDecoder->skipScanlines(subsetStartY);