Add failing test for FontCacheTask::add_web_font

This test tries to add a web font to the `FontCacheTask`. The added web font
corresponds to the following CSS font definition:

```
@font-face {
  font-family: "test family";
  src: local(test font face);
}
```

This test fails, since `FontCacheTask` tries to get the value for the key
"test font face" from `self.web_families`, but previously initialized
a value for the key "test family".

components/servo/Cargo.lock

@@ -650,6 +650,8 @@ name = "gfx_tests"
 version = "0.0.1"
 dependencies = [
  "gfx 0.0.1",
+ "ipc-channel 0.1.0 (git+https://github.com/servo/ipc-channel)",
+ "style 0.0.1",
 ]
 
 [[package]]

tests/unit/gfx/Cargo.toml

@@ -10,3 +10,9 @@ doctest = false
 
 [dependencies.gfx]
 path = "../../../components/gfx"
+
+[dependencies.ipc-channel]
+git = "https://github.com/servo/ipc-channel"
+
+[dependencies.style]
+path = "../../../components/style"

tests/unit/gfx/font_cache_task.rs

@@ -0,0 +1,21 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use gfx::font_cache_task::FontCacheTask;
+use ipc_channel::ipc;
+use style::computed_values::font_family::FontFamily;
+use style::font_face::Source;
+
+#[test]
+fn test_local_web_font() {
+  let (inp_chan, _) = ipc::channel().unwrap();
+  let (out_chan, out_receiver) = ipc::channel().unwrap();
+  let font_cache_task = FontCacheTask::new(inp_chan);
+  let family_name = FontFamily::FamilyName(From::from("test family"));
+  let variant_name = FontFamily::FamilyName(From::from("test font face"));
+
+  font_cache_task.add_web_font(family_name, Source::Local(variant_name), out_chan);
+
+  assert_eq!(out_receiver.recv().unwrap(), ());
+}

tests/unit/gfx/lib.rs

@@ -3,5 +3,8 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 extern crate gfx;
+extern crate ipc_channel;
+extern crate style;
 
+#[cfg(test)] mod font_cache_task;
 #[cfg(test)] mod text_util;