[Chromecast] Replace 'fontconfig' GN target with dynamic dependency.

Chromecast needs to be able to optionally use //third_party/fontconfig
instead of system headers. This CL acheives parity with the GYP build
for this feature:
https://code.google.com/p/chromium/codesearch#chromium/src/build/linux/system.gyp&l=748

BUG=516899

Review URL: https://codereview.chromium.org/1366653003

Cr-Commit-Position: refs/heads/master@{#350711}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index e4342e0..6100eb2 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -799,11 +799,11 @@
     sources +=
         rebase_path(gypi_values.chrome_browser_linux_sources, ".", "//chrome")
     if (use_aura) {
-      configs += [
-        "//build/config/linux:dbus",
-        "//build/config/linux:fontconfig",
+      configs += [ "//build/config/linux:dbus" ]
+      deps += [
+        "//build/linux:fontconfig",
+        "//dbus",
       ]
-      deps += [ "//dbus" ]
     }
     if (use_x11) {
       configs += [ "//build/config/linux:x11" ]