Bug 1607697 - Allow excessive precision in debug color constants. r=G…

…ankro

Addresses a clippy lint.

Differential Revision: https://phabricator.services.mozilla.com/D59113

[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/fddd2d637eb0d4a842c465547447616762831043

webrender/src/debug_colors.rs

@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #![allow(dead_code)]
+#![cfg_attr(feature = "cargo-clippy", allow(clippy::excessive_precision))]
 
 use api::ColorF;