tuned skiaserve's png output for better performance

gyp/skiaserve.gyp

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 # GYP file to build performance testbench.
 #
 {
   'includes': [
     'apptype_console.gypi',
   ],
@@ skipping 17 matching lines @@
         '../tools/debugger/SkObjectParser.cpp',
         '../tools/debugger/SkOverdrawMode.h',
         '../tools/debugger/SkOverdrawMode.cpp',
         '<!@(python find.py ../tools/skiaserve "*.cpp")',
       ],
       'dependencies': [
         'flags.gyp:flags',
         'gputest.gyp:skgputest',
         'json.gyp:json',
         'jsoncpp.gyp:jsoncpp',
+        'libpng.gyp:libpng',
         'microhttpd.gyp:microhttpd',
         'skia_lib.gyp:skia_lib',
         'tools.gyp:crash_handler',
         'tools.gyp:proc_stats',
         'tools.gyp:resources',
         'tools.gyp:url_data_manager',
       ],
     },
   ],
 }