Auto merge of #15167 - heycam:cssparser-up-2, r=bholley

Update cssparser to 0.7.3 to get perf improvements.

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components/style/Cargo.toml

@@ -26,7 +26,7 @@ app_units = "0.3"
 atomic_refcell = "0.1"
 bitflags = "0.7"
 cfg-if = "0.1.0"
-cssparser = "0.7"
+cssparser = "0.7.3"
 encoding = "0.2"
 euclid = "0.10.1"
 fnv = "1.0"