Update euclid.

There are a few canvas2d-related dependencies that haven't updated, but they
only use euclid internally so that's not blocking landing the rest of the
changes.

Given the size of this patch, I think it's useful to get this landed as-is.

components/geometry/lib.rs

@@ -6,7 +6,10 @@
 extern crate malloc_size_of_derive;
 
 use app_units::{Au, MAX_AU, MIN_AU};
-use euclid::{Length, Point2D, Rect, Size2D};
+use euclid::{
+    default::{Point2D, Rect, Size2D},
+    Length,
+};
 use std::f32;
 use webrender_api::units::{FramebufferPixel, LayoutPoint, LayoutRect, LayoutSize};