Merge branch 'material' into 'master'

fix mistakes in merge

See merge request upm-packages/ui-widgets/com.unity.uiwidgets!58

Runtime/ui/txt/paragraph.cs

         }
 
         public List<TextBox> getRectsForRange(int start, int end) {
-            var lineBoxes = new SortedDictionary<int, List<TextBox>>();
+            var lineBoxes = new SplayTree<int, List<TextBox>>();
             foreach (var run in this._codeUnitRuns) {
                 if (run.codeUnits.start >= end) {
                     break;

Runtime/widgets/sliver.cs

 using Unity.UIWidgets.foundation;
 using Unity.UIWidgets.painting;
 using Unity.UIWidgets.rendering;
+using Unity.UIWidgets.ui;
 
 namespace Unity.UIWidgets.widgets {
     public abstract class SliverChildDelegate {
         }
 
         Dictionary<int, Widget> _childWidgets = new Dictionary<int, Widget>();
-        SortedDictionary<int, Element> _childElements = new SortedDictionary<int, Element>();
+        SplayTree<int, Element> _childElements = new SplayTree<int, Element>();
         RenderBox _currentBeforeChild;
 
         protected override void performRebuild() {
                 int lastIndex = 0;
 
                 if (!this._childElements.isEmpty()) {
-                    firstIndex = this._childElements.Keys.First();
-                    lastIndex = this._childElements.Keys.Last();
+                    firstIndex = this._childElements.First().Key;
+                    lastIndex = this._childElements.Last().Key;
                     if (this._didUnderflow) {
                         lastIndex += 1;
                     }
 
         public void didFinishLayout() {
             D.assert(this.debugAssertChildListLocked());
-            int firstIndex = this._childElements.Keys.FirstOrDefault();
-            int lastIndex = this._childElements.Keys.LastOrDefault();
+            int firstIndex = this._childElements.FirstOrDefault().Key;
+            int lastIndex = this._childElements.LastOrDefault().Key;
             this.widget.del.didFinishLayout(firstIndex, lastIndex);
         }