Auto merge of #18310 - nnethercote:bug-1394729, r=heycam

Measure memory usage of Stylo's Rule Tree.

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This is for https://bugzilla.mozilla.org/show_bug.cgi?id=1394729, which was r=heycam.

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

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because tests exist in Gecko.

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components/style/gecko/generated/bindings.rs

@@ -61,6 +61,7 @@ use gecko_bindings::structs::SeenPtrs;
 use gecko_bindings::structs::ServoBundledURI;
 use gecko_bindings::structs::ServoElementSnapshot;
 use gecko_bindings::structs::ServoElementSnapshotTable;
+use gecko_bindings::structs::ServoStyleSetSizes;
 use gecko_bindings::structs::SheetParsingMode;
 use gecko_bindings::structs::StyleBasicShape;
 use gecko_bindings::structs::StyleBasicShapeType;
@@ -2067,6 +2068,11 @@ extern "C" {
                                                      RawServoDeclarationBlockBorrowed)
      -> ServoStyleContextStrong;
 }
+extern "C" {
+    pub fn Servo_StyleSet_AddSizeOfExcludingThis(malloc_size_of: MallocSizeOf,
+                                                 sizes: *mut ServoStyleSetSizes,
+                                                 set: RawServoStyleSetBorrowed);
+}
 extern "C" {
     pub fn Servo_StyleContext_AddRef(ctx: ServoStyleContextBorrowed);
 }