Make skia_use_xps option work on Windows

Some may not want to always compile XPS on Windows

Change-Id: Icd4cc993667fdce740216b9c52a0a649dcf79645
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/278782
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index b4822ef..b457731 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -724,6 +724,7 @@
   if (skia_use_libjpeg_turbo_encode) {
     deps += [ ":jpeg_encode" ]
   }
+  public = skia_pdf_public
   sources = skia_pdf_sources
   sources_when_disabled = [ "src/pdf/SkDocument_PDF_None.cpp" ]
   if (skia_use_icu && skia_use_harfbuzz && skia_pdf_subset_harfbuzz) {
@@ -735,6 +736,13 @@
   }
 }
 
+optional("xps") {
+  enabled = skia_use_xps && is_win
+  public_defines = [ "SK_SUPPORT_XPS" ]
+  public = skia_xps_public
+  sources = skia_xps_sources
+}
+
 optional("png_decode") {
   enabled = skia_use_libpng_decode
   public_defines = [ "SK_CODEC_DECODES_PNG" ]
@@ -904,6 +912,7 @@
     ":gpu",
     ":pdf",
     ":skcms",
+    ":xps",
   ]
 
   deps = [
@@ -951,14 +960,10 @@
   public += skia_utils_public
   public += skia_effects_public
   public += skia_effects_imagefilter_public
-  public += skia_xps_public
 
   sources = []
   sources += skia_core_sources
   sources += skia_utils_sources
-  if (skia_use_xps) {
-    sources += skia_xps_sources
-  }
   sources += skia_effects_sources
   sources += skia_effects_imagefilter_sources
   sources += skia_sksl_sources