Android U Beta 1 GPL
Merge "Upgrade libpng to v1.6.39" am: cb9e209cab

Original change: https://android-review.googlesource.com/c/platform/external/libpng/+/2435872

Change-Id: I55f6baed19a6ba4cbb67fbd493e1615e9570cef9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>