LibWeb: Revert changing transform's animation-type to by-computed-value

In the upcoming commits where we properly handle transformation
interpolation, it actually becomes easier to change this back to custom,
so lets do that since its more correct anyways.

Userland/Libraries/LibWeb/CSS/Properties.json

@@ -2231,7 +2231,7 @@
     ]
   },
   "transform": {
-    "animation-type": "by-computed-value",
+    "animation-type": "custom",
     "inherited": false,
     "initial": "none",
     "affects-layout": false,

Userland/Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -811,24 +811,8 @@ static ErrorOr<NonnullRefPtr<StyleValue const>> interpolate_value(StyleValue con
             Length(interpolate_raw(from_rect.left_edge.raw_value(), to_rect.left_edge.raw_value()), from_rect.left_edge.type()),
         });
     }
-    case StyleValue::Type::Transformation: {
-        auto& from_transform = from.as_transformation();
-        auto& to_transform = to.as_transformation();
-        if (from_transform.transform_function() != to_transform.transform_function())
-            return from;
-
-        auto from_input_values = from_transform.values();
-        auto to_input_values = to_transform.values();
-        if (from_input_values.size() != to_input_values.size())
-            return from;
-
-        StyleValueVector interpolated_values;
-        interpolated_values.ensure_capacity(from_input_values.size());
-        for (size_t i = 0; i < from_input_values.size(); ++i)
-            interpolated_values.append(TRY(interpolate_value(*from_input_values[i], *to_input_values[i], delta)));
-
-        return TransformationStyleValue::create(from_transform.transform_function(), move(interpolated_values));
-    }
+    case StyleValue::Type::Transformation:
+        VERIFY_NOT_REACHED();
     case StyleValue::Type::ValueList: {
         auto& from_list = from.as_value_list();
         auto& to_list = to.as_value_list();
@@ -861,8 +845,31 @@ static ErrorOr<ValueComparingNonnullRefPtr<StyleValue const>> interpolate_proper
         return interpolate_value(from, to, delta);
     case AnimationType::None:
         return to;
-    // FIXME: Handle all custom animatable properties
-    case AnimationType::Custom:
+    case AnimationType::Custom: {
+        if (property_id == PropertyID::Transform) {
+            // Try to optimize same-function interpolation
+            if (from.is_transformation() && to.is_transformation()) {
+                auto& from_transform = from.as_transformation();
+                auto& to_transform = to.as_transformation();
+                if (from_transform.transform_function() == to_transform.transform_function()) {
+                    auto from_input_values = from_transform.values();
+                    auto to_input_values = to_transform.values();
+                    if (from_input_values.size() == to_input_values.size()) {
+                        StyleValueVector interpolated_values;
+                        interpolated_values.ensure_capacity(from_input_values.size());
+                        for (size_t i = 0; i < from_input_values.size(); ++i)
+                            interpolated_values.append(TRY(interpolate_value(element, *from_input_values[i], *to_input_values[i], delta)));
+
+                        return TransformationStyleValue::create(from_transform.transform_function(), move(interpolated_values));
+                    }
+                }
+            }
+            return from;
+        }
+
+        // FIXME: Handle all custom animatable properties
+        [[fallthrough]];
+    }
     // FIXME: Handle repeatable-list animatable properties
     case AnimationType::RepeatableList:
     case AnimationType::Discrete: