gn: Fix build issues blocking gfx from being built

third_party/libpng/BUILD.gn

Index: third_party/libpng/BUILD.gn
diff --git a/third_party/libpng/BUILD.gn b/third_party/libpng/BUILD.gn
index f920c0ba3cb8e88d79c7055104941836332eac75..fdfd5a6a79b6d30291d617289fc8638217dc2902 100644
--- a/third_party/libpng/BUILD.gn
+++ b/third_party/libpng/BUILD.gn
@@ -29,7 +29,7 @@ config("libpng_config") {
   }
 }
 
-static_library("libpng") {
+source_set("libpng_sources") {
   sources =  [
     "png.c",
     "png.h",
@@ -58,6 +58,10 @@ static_library("libpng") {
 
   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" ]
@@ -68,3 +72,17 @@ static_library("libpng") {
     "//third_party/zlib",
   ]
 }
+
+if (is_win) {
+  component("libpng") {
+    deps = [ ":libpng_sources" ]
+
+    forward_dependent_configs_from = [ ":libpng_sources" ]

[brettw, 2014/09/21 02:55:00]

I'm trying to get rid of this. Replace "deps" with "public_deps" and it means
the same things as deps + forward. Same below.

[ckocagil, 2014/09/21 11:47:26]

Done.

+  }
+} else {
+  static_library("libpng") {
+    deps = [ ":libpng_sources" ]
+
+    forward_dependent_configs_from = [ ":libpng_sources" ]
+  }
+}