Split Au type into separate crate, with minimal dependencies.

components/compositing/Cargo.toml

@@ -7,6 +7,9 @@ authors = ["The Servo Project Developers"]
 name = "compositing"
 path = "lib.rs"
 
+[dependencies.app_units]
+path = "../app_units"
+
 [dependencies.gfx]
 path = "../gfx"
 

components/compositing/compositor.rs

@@ -2,6 +2,7 @@
  * 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 app_units::Au;
 use compositor_layer::{CompositorData, CompositorLayer, RcCompositorLayer, WantsScrollEventsFlag};
 use compositor_task::{CompositorEventListener, CompositorProxy};
 use compositor_task::{CompositorReceiver, InitialCompositorState, Msg};
@@ -46,7 +47,7 @@ use style_traits::viewport::ViewportConstraints;
 use surface_map::SurfaceMap;
 use time::{precise_time_ns, precise_time_s};
 use url::Url;
-use util::geometry::{Au, PagePx, ScreenPx, ViewportPx};
+use util::geometry::{PagePx, ScreenPx, ViewportPx};
 use util::opts;
 use windowing::{self, MouseWindowEvent, WindowEvent, WindowMethods, WindowNavigateMsg};
 

components/compositing/lib.rs

@@ -11,6 +11,7 @@
 
 #![deny(unsafe_code)]
 
+extern crate app_units;
 #[macro_use]
 extern crate log;
 #[macro_use]