Add missing fontconfig build dependency to Skia builds on Linux.

Skia on Linux uses fontconfig. Add the required GN rule to satisfy this
dependency.

Change-Id: I4ee4fd2ae8446936297cc0ae69d73a7650a717b5
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/91111
Reviewed-by: Nigi <nigi@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

skia/BUILD.gn

diff --git a/skia/BUILD.gn b/skia/BUILD.gn
index b225bcd..343a59c 100644
--- a/skia/BUILD.gn
+++ b/skia/BUILD.gn
@@ -323,7 +323,10 @@
   public_deps = [ ":skia_core_and_effects" ]
 
   if (is_linux || is_chromeos) {
-    deps += [ "//third_party/icu:icuuc" ]
+    deps += [
+      "//third_party:fontconfig",
+      "//third_party/icu:icuuc",
+    ]
   }
 
   if (is_android) {

third_party/BUILD.gn

diff --git a/third_party/BUILD.gn b/third_party/BUILD.gn
index 63ec66e..6527102 100644
--- a/third_party/BUILD.gn
+++ b/third_party/BUILD.gn
@@ -200,7 +200,14 @@
   }
 }
 
-if (!pdf_use_skia && !pdf_use_skia_paths) {
+if (pdf_use_skia || pdf_use_skia_paths) {
+  config("system_fontconfig") {
+    libs = [ "fontconfig" ]
+  }
+  group("fontconfig") {
+    public_configs = [ ":system_fontconfig" ]
+  }
+} else {
   config("fx_agg_warnings") {
     visibility = [ ":*" ]
     if (is_clang) {