Auto merge of #12571 - servo:selectors-generic-atom_, r=bholley

Update to selectors 0.8.2 (generic over atoms)

This removes the `[replace]` override in geckolib and therefore unblocks https://github.com/servo/servo/pull/12391.

This includes the `gecko_string_cache` redesign discussed in https://github.com/servo/servo/pull/12548.

r? @bholley

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #12548 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [x] These changes do not require new tests because refactor

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components/layout/Cargo.toml

@@ -33,7 +33,7 @@ range = {path = "../range"}
 rustc-serialize = "0.3"
 script_layout_interface = {path = "../script_layout_interface"}
 script_traits = {path = "../script_traits"}
-selectors = {version = "0.7", features = ["heap_size"]}
+selectors = {version = "0.8", features = ["heap_size"]}
 serde_macros = "0.7.15"
 smallvec = "0.1"
 string_cache = {version = "0.2.20", features = ["heap_size"]}

components/layout/traversal.rs

@@ -27,7 +27,7 @@ pub struct RecalcStyleAndConstructFlows<'lc> {
 
 impl<'lc, N> DomTraversalContext<N> for RecalcStyleAndConstructFlows<'lc>
     where N: LayoutNode + TNode,
-          N::ConcreteElement: ::selectors::Element<Impl=ServoSelectorImpl, AttrString=String>
+          N::ConcreteElement: ::selectors::Element<Impl=ServoSelectorImpl>
 
 {
     type SharedContext = SharedLayoutContext;