gn: Fix build issues blocking gfx from being built

third_party/libpng/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 config("libpng_config") {
   include_dirs = [
     ".",
   ]
 
   defines = [
@@ skipping 11 matching lines @@
   if (is_win) {
     if (component_mode == "shared_library") {
       defines += [
         "PNG_USE_DLL",
         "PNG_NO_MODULEDEF",
       ]
     }
   }
 }
 
-static_library("libpng") {
+source_set("libpng_sources") {
   sources =  [
     "png.c",
     "png.h",
     "pngconf.h",
     "pngerror.c",
     "pnggccrd.c",
     "pngget.c",
     "pngmem.c",
     "pngpread.c",
     "pngread.c",
     "pngrio.c",
     "pngrtran.c",
     "pngrutil.c",
     "pngset.c",
     "pngtrans.c",
     "pngusr.h",
     "pngvcrd.c",
     "pngwio.c",
     "pngwrite.c",
     "pngwtran.c",
     "pngwutil.c",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
 
   if (is_win) {
     cflags = [ "/wd4267" ]  # TODO(jschuh): http://crbug.com/167187
+
+    if (component_mode == "shared_library") {
+      defines = [ "PNG_BUILD_DLL" ]
+    }
   }
 
-  forward_dependent_configs_from = [ "//third_party/zlib" ]
-
   direct_dependent_configs = [ ":libpng_config" ]
 
-  deps =  [
-    "//third_party/zlib",
-  ]
+  public_deps = [ "//third_party/zlib" ]
 }
+
+if (is_win) {
+  component("libpng") {
+    public_deps = [ ":libpng_sources" ]
+  }
+} else {
+  static_library("libpng") {
+    public_deps = [ ":libpng_sources" ]
+  }
+}