servo: Merge #7097 - Measure heap memory usage for more types. Fixes #6951 (from boghison:memtypes); r=jdm

Also adds HeapSizeOf implementations/derive for some types. I've used "Cannot calculate Heap size" as a reason everywhere, because my imagination is rather limited. If you'd like me to change this message for specific types, please write something like this: "Trusted - Cannot calculate Heap size for Trusted" so that it would be easier for me to replace them through a script :)

Source-Repo: https://github.com/servo/servo
Source-Revision: a03616f379c255cc6c9b6e1d04dd7d98bd9926ce

servo/components/msg/constellation_msg.rs

@@ -19,6 +19,7 @@ use offscreen_gl_context::GLContextAttributes;
 use png::Image;
 use util::cursor::Cursor;
 use util::geometry::{PagePx, ViewportPx};
+use util::mem::HeapSizeOf;
 use std::collections::HashMap;
 use std::sync::mpsc::{channel, Sender, Receiver};
 use style::viewport::ViewportConstraints;
@@ -69,7 +70,7 @@ pub enum KeyState {
 }
 
 //N.B. Based on the glutin key enum
-#[derive(Debug, PartialEq, Eq, Copy, Clone, Deserialize, Serialize)]
+#[derive(Debug, PartialEq, Eq, Copy, Clone, Deserialize, Serialize, HeapSizeOf)]
 pub enum Key {
     Space,
     Apostrophe,