Update from https://crrev.com/317530

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 488ef4367f8264762257ce5bc8906cc48a2ecfac..787d4fa7d00ecb3b5e0dd237dd4cec24aa5d5a0e 100644
--- a/third_party/libpng/BUILD.gn
+++ b/third_party/libpng/BUILD.gn
@@ -52,12 +52,8 @@ source_set("libpng_sources") {
   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" ]
-    }
+  if (is_win && is_component_build) {
+    defines = [ "PNG_BUILD_DLL" ]
   }
 
   public_configs = [ ":libpng_config" ]