LibWeb: Handle steps(x, start) like steps(x, jump-start)

Author: https://github.com/Gingeh
Commit: https://github.com/LadybirdBrowser/ladybird/commit/cd5d8f4d95b
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2173
Reviewed-by: https://github.com/AtkinsSJ ✅

Tests/LibWeb/Text/expected/WebAnimations/misc/easing-values.txt

@@ -178,6 +178,18 @@ cubic-bezier(1, 1000, 1, 1000)
 80: 1.00
 90: 1.00
 100: 1.00
+step-start
+0: 1.00
+10: 1.00
+20: 1.00
+30: 1.00
+40: 1.00
+50: 1.00
+60: 1.00
+70: 1.00
+80: 1.00
+90: 1.00
+100: 1.00
 step-end
 0: 0.00
 10: 0.00
@@ -250,6 +262,18 @@ steps(10, jump-both)
 80: 0.82
 90: 0.91
 100: 1.00
+steps(10, start)
+0: 0.10
+10: 0.20
+20: 0.30
+30: 0.40
+40: 0.50
+50: 0.60
+60: 0.70
+70: 0.80
+80: 0.90
+90: 1.00
+100: 1.00
 steps(10, end)
 0: 0.00
 10: 0.10

Tests/LibWeb/Text/input/WebAnimations/misc/easing-values.html

@@ -21,14 +21,14 @@
             "cubic-bezier(0, 0, 0, 0)",
             "cubic-bezier(1, 1, 1, 1)",
             "cubic-bezier(1, 1000, 1, 1000)",
-            // FIXME: "step-start",
+            "step-start",
             "step-end",
             "steps(1000)",
             "steps(10, jump-start)",
             "steps(10, jump-end)",
             "steps(10, jump-none)",
             "steps(10, jump-both)",
-            // FIXME: "steps(10, start)",
+            "steps(10, start)",
             "steps(10, end)",
         ];
 

Userland/Libraries/LibWeb/CSS/StyleValues/EasingStyleValue.cpp

@@ -342,7 +342,7 @@ double EasingStyleValue::Steps::evaluate_at(double input_progress, bool before_f
     //    - jump-start,
     //    - jump-both,
     //    increment current step by one.
-    if (position == Steps::Position::JumpStart || position == Steps::Position::JumpBoth)
+    if (position == Steps::Position::JumpStart || position == Steps::Position::Start || position == Steps::Position::JumpBoth)
         current_step += 1;
 
     // 3. If both of the following conditions are true: