Updated chromium-browser-stable/libpng packages fix security vulnerability

Chromium-browser-stable 51.0.2704.79 fixes security issues: cross-origin bypass problems in extension bindings (CVE-2016-1696) and blink (CVE-2016-1697), an information leak in extension bindings (CVE-2016-1698), a parameter sanitization failure in devtools (CVE-2016-1699), use-after-free bugs in extensions (CVE-2016-1700) and autofill (CVE-2016-1701), an out-of-bounds read in skia (CVE-2016-1702), and various fixes from upstream’s internal audits, fuzzing, and other initiatives (CVE-2016-1703).