Auto merge of #15175 - BorisChiou:animation/interpolate_and_cascade, r=heycam

Interpolate servo animation values and add them to the cascade

These are the servo-side changes for [bug 1317209](https://bugzilla.mozilla.org/show_bug.cgi?id=1317209). @Manishearth, @emilio, and @heycam have already reviewed them there. Please merge these patches until the gecko-side changes for [bug 1317209](https://bugzilla.mozilla.org/show_bug.cgi?id=1317209) is landed.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [bug 1317209](https://bugzilla.mozilla.org/show_bug.cgi?id=1317209).
- [X] These changes do not require tests because there are existing tests for this in mozilla-central

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ports/geckolib/glue.rs

@@ -39,6 +39,8 @@ use style::gecko_bindings::bindings::RawGeckoAnimationValueListBorrowedMut;
 use style::gecko_bindings::bindings::RawGeckoElementBorrowed;
 use style::gecko_bindings::bindings::RawGeckoPresContextBorrowed;
 use style::gecko_bindings::bindings::RawServoAnimationValueBorrowed;
+use style::gecko_bindings::bindings::RawServoAnimationValueBorrowedListBorrowed;
+use style::gecko_bindings::bindings::RawServoAnimationValueStrong;
 use style::gecko_bindings::bindings::RawServoImportRuleBorrowed;
 use style::gecko_bindings::bindings::ServoComputedValuesBorrowedOrNull;
 use style::gecko_bindings::bindings::nsTArrayBorrowed_uintptr_t;
@@ -58,7 +60,7 @@ use style::parser::{ParserContext, ParserContextExtraData};
 use style::properties::{CascadeFlags, ComputedValues, Importance, PropertyDeclaration};
 use style::properties::{PropertyDeclarationParseResult, PropertyDeclarationBlock, PropertyId};
 use style::properties::{apply_declarations, parse_one_declaration};
-use style::properties::animated_properties::AnimationValue;
+use style::properties::animated_properties::{AnimationValue, Interpolate};
 use style::restyle_hints::RestyleHint;
 use style::selector_parser::PseudoElementCascadeType;
 use style::sequential;
@@ -165,6 +167,39 @@ pub extern "C" fn Servo_TraverseSubtree(root: RawGeckoElementBorrowed,
                      behavior == structs::TraversalRootBehavior::UnstyledChildrenOnly);
 }
 
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValues_Interpolate(from: RawServoAnimationValueBorrowed,
+                                                    to: RawServoAnimationValueBorrowed,
+                                                    progress: f64)
+     -> RawServoAnimationValueStrong
+{
+    let from_value = AnimationValue::as_arc(&from);
+    let to_value = AnimationValue::as_arc(&to);
+    if let Ok(value) = from_value.interpolate(to_value, progress) {
+        Arc::new(value).into_strong()
+    } else {
+        RawServoAnimationValueStrong::null()
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValues_Uncompute(value: RawServoAnimationValueBorrowedListBorrowed)
+     -> RawServoDeclarationBlockStrong
+{
+    let uncomputed_values = value.into_iter()
+                                 .map(|v| {
+                                     let raw_anim = unsafe { v.as_ref().unwrap() };
+                                     let anim = AnimationValue::as_arc(&raw_anim);
+                                     (anim.uncompute(), Importance::Normal)
+                                 })
+                                 .collect();
+
+    Arc::new(RwLock::new(PropertyDeclarationBlock {
+        declarations: uncomputed_values,
+        important_count: 0,
+    })).into_strong()
+}
+
 /// Takes a ServoAnimationValues and populates it with the animation values corresponding
 /// to a given property declaration block
 #[no_mangle]