Use the bundled fontconfig for ui/gfx_unittests

The target gfx_unittests used the system's fontconfig which
stopped working on Ubuntu 16.04 without sysroot when the tests
started using FcConfigParseAndLoadFromMemory which is a
newly (2017) added fontconfig function.

The test should have used third_party/fontconfig all the time
but the test didn't have the necessary deps in the build system
for that to happen.

Follow-up to https://chromium-review.googlesource.com/c/1019978

Change-Id: Ie0dab4632aff454b6c33405d3076c87e226b7e18
Reviewed-on: https://chromium-review.googlesource.com/c/1489237
Commit-Queue: Daniel Bratell <bratell@opera.com>
Commit-Queue: Nico Weber <thakis@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Auto-Submit: Daniel Bratell <bratell@opera.com>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635569}
diff --git a/ui/gfx/BUILD.gn b/ui/gfx/BUILD.gn
index 78256bdf..98ef95f 100644
--- a/ui/gfx/BUILD.gn
+++ b/ui/gfx/BUILD.gn
@@ -792,6 +792,7 @@
 
   if (is_linux) {
     sources += [ "linux/native_pixmap_dmabuf_unittest.cc" ]
+    deps += [ "//third_party/fontconfig" ]
   }
 }