Fix png encoding in skia debugger

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2119513002

Review-Url: https://codereview.chromium.org/2119513002
diff --git a/gyp/debugger.gyp b/gyp/debugger.gyp
index 9a460db..dcc6f44 100644
--- a/gyp/debugger.gyp
+++ b/gyp/debugger.gyp
@@ -140,6 +140,7 @@
         'skia_lib.gyp:skia_lib',
         'jsoncpp.gyp:jsoncpp',
         'libpng.gyp:libpng',
+        'tools.gyp:picture_utils',
         'tools.gyp:url_data_manager',
       ],
       'cflags': [