Update libpng to 1.6.22beta

Intel SSE filter optimizations have been upstreamed.  Let's test on
the upstream version (which we can use in Android).

BUG=skia:4573
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1710083007

Review URL: https://codereview.chromium.org/1710083007
diff --git a/DEPS b/DEPS
index c98b3fd..58fc188 100644
--- a/DEPS
+++ b/DEPS
@@ -18,7 +18,7 @@
   "third_party/externals/nanomsg" : "https://skia.googlesource.com/third_party/nanomsg.git@0.4-beta",
   "third_party/externals/zlib"    : "https://chromium.googlesource.com/chromium/src/third_party/zlib@c4e33043fb071b6ea0a153845da625d7ed633d3d",
   # NOTE: If we update libpng, we may need to update the generated file at third_party/libpng/pnglibconf.h
-  "third_party/externals/libpng"  : "https://skia.googlesource.com/third_party/libpng.git@047737496a77eeb97f9991919dac08ca3c149711",
+  "third_party/externals/libpng"  : "https://skia.googlesource.com/third_party/libpng.git@52846504da1f519cf1bb89636caf9110e8677443",
   "third_party/externals/giflib"  : "https://android.googlesource.com/platform/external/giflib.git@ab10e256df4f684260ca239905b1cec727181f6c",
 
   "third_party/externals/dng_sdk" : "https://android.googlesource.com/platform/external/dng_sdk.git@6579353b8ee5d8aa1f1a96ae22798de9b41e19b8",