Duplicate first gradient stop if necessary.

If the first stop of a non-repeating gradient is
not placed at offset 0.0 it is duplicated at this
position. This solves the problem of the first
stop being ignored if it is placed at the same
offset as the next stop.

components/layout/display_list_builder.rs

@@ -650,8 +650,8 @@ fn convert_gradient_stops(gradient_items: &[GradientItem],
     }
 
     // Step 3: Evenly space stops without position.
-    // Note: Remove the + 1 if fix_gradient_stops is changed.
-    let mut stops = Vec::with_capacity(stop_items.len() + 1);
+    // Note: Remove the + 2 if fix_gradient_stops is changed.
+    let mut stops = Vec::with_capacity(stop_items.len() + 2);
     let mut stop_run = None;
     for (i, stop) in stop_items.iter().enumerate() {
         let offset = match stop.position {
@@ -698,15 +698,25 @@ fn convert_gradient_stops(gradient_items: &[GradientItem],
 }
 
 #[inline]
-/// Duplicate the last stop if its position is smaller 100%.
+/// Duplicate the first and last stops if necessary.
 ///
 /// Explanation by pyfisch:
 /// If the last stop is at the same position as the previous stop the
 /// last color is ignored by webrender. This differs from the spec
 /// (I think so). The  implementations of Chrome and Firefox seem
 /// to have the same problem but work fine if the position of the last
 /// stop is smaller than 100%. (Otherwise they ignore the last stop.)
+///
+/// Similarly the first stop is duplicated if it is not placed
+/// at the start of the virtual gradient ray.
 fn fix_gradient_stops(stops: &mut Vec<GradientStop>) {
+    if stops.first().unwrap().offset > 0.0 {
+        let color = stops.first().unwrap().color;
+        stops.insert(0, GradientStop {
+            offset: 0.0,
+            color: color,
+        })
+    }
     if stops.last().unwrap().offset < 1.0 {
         let color = stops.last().unwrap().color;
         stops.push(GradientStop {