Auto merge of #18649 - nnethercote:bug-1400459, r=froydnj

Devirtualize nsIAtom.

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https://bugzilla.mozilla.org/show_bug.cgi?id=1400459
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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 https://bugzilla.mozilla.org/show_bug.cgi?id=1400459

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because tested on the Gecko side.

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components/style/values/specified/font.rs

@@ -168,7 +168,6 @@ impl ToComputedValue for KeywordSize {
     type ComputedValue = NonNegativeLength;
     #[inline]
     fn to_computed_value(&self, cx: &Context) -> NonNegativeLength {
-        use gecko_bindings::structs::nsIAtom;
         use values::specified::length::au_to_int_px;
         // Data from nsRuleNode.cpp in Gecko
         // Mapping from base size and HTML size to pixels
@@ -194,7 +193,7 @@ impl ToComputedValue for KeywordSize {
         // XXXManishearth handle quirks mode (bug 1401322)
 
         let ref gecko_font = cx.style().get_font().gecko();
-        let base_size = unsafe { Atom::with(gecko_font.mLanguage.raw::<nsIAtom>(), |atom| {
+        let base_size = unsafe { Atom::with(gecko_font.mLanguage.mRawPtr, |atom| {
             cx.font_metrics_provider.get_size(atom, gecko_font.mGenericID).0
         }) };