Measure PropertyDeclaration more thoroughly.

This patch replaces the handwritten MallocSizeOf implementation for
PropertyDeclaration with a derived one, which gives much more thorough
measurement.

This requires (a) deriving MallocSizeOf for a *lot* of additional types (most
of which already have `derive(HeapSizeOf)` in Servo builds), and (b)
implementing MallocSizeOf for a few more types in the `malloc_size_of` crate.

These changes would significantly improve the reporting coverage for gmail if
it weren't for the fact that SpecifiedUrl isn't measured due to a lack of
clarity about its fields; that can be fixed as a follow-up once bug 1397971 has
landed.

components/malloc_size_of/Cargo.toml

@@ -9,6 +9,9 @@ publish = false
 path = "lib.rs"
 
 [dependencies]
+app_units = "0.5.5"
+cssparser = "0.21.0"
+euclid = "0.15"
 hashglobe = { path = "../hashglobe" }
 servo_arc = { path = "../servo_arc" }
 smallbitvec = "1.0.3"