Fixing MAS Compliance Issues (#1278)

* Ensuring GroupItemAutomationPeer adds underlying ExpanderPeer to its list of children peers

* Enabling ScrollPattern only when Combobox dropDown is opened

* Addressing PR feedback

Author: arpitmathur

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Automation/Peers/ComboBoxAutomationPeer.cs

@@ -51,16 +51,20 @@ override protected string GetClassNameCore()
         override public object GetPattern(PatternInterface pattern)
         {
             object iface = null;
+            ComboBox owner = (ComboBox)Owner;
 
             if (pattern == PatternInterface.Value)
             {
-                ComboBox owner = (ComboBox)Owner;
                 if (owner.IsEditable) iface = this;
             }
             else if(pattern == PatternInterface.ExpandCollapse)
             {
                 iface = this;
             }
+            else if (pattern == PatternInterface.Scroll && !owner.IsDropDownOpen)
+            {
+                iface = this;
+            }
             else
             {
                 iface = base.GetPattern(pattern);

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Automation/Peers/GroupItemAutomationPeer.cs

@@ -130,14 +130,7 @@ protected override List<AutomationPeer> GetChildrenCore()
                 ItemsControlAutomationPeer itemsControlAP = itemsControl.CreateAutomationPeer() as ItemsControlAutomationPeer;
                 if (itemsControlAP != null)
                 {
-                    Panel itemsHost = owner.ItemsHost;
-
-                    if (itemsHost == null)
-                        return null;
-
-                    IList childItems = itemsHost.Children;
-                    List<AutomationPeer> children = new List<AutomationPeer>(childItems.Count);
-                    ItemPeersStorage<ItemAutomationPeer> addedChildren = new ItemPeersStorage<ItemAutomationPeer>();
+                    List<AutomationPeer> children = new List<AutomationPeer>();
                     bool useNetFx472CompatibleAccessibilityFeatures = AccessibilitySwitches.UseNetFx472CompatibleAccessibilityFeatures;
 
                     if (!useNetFx472CompatibleAccessibilityFeatures && owner.Expander != null)
@@ -152,6 +145,24 @@ protected override List<AutomationPeer> GetChildrenCore()
                             _expanderPeer.GetChildren();
                         }
                     }
+                    Panel itemsHost = owner.ItemsHost;
+
+                    if (itemsHost == null)
+                    {
+                        if (_expanderPeer == null)
+                        {
+                            return null;
+                        }
+                        else
+                        {
+                            children.Add(_expanderPeer);
+                            return children;
+                        }
+                    }
+                        
+                    IList childItems = itemsHost.Children;
+                    ItemPeersStorage<ItemAutomationPeer> addedChildren = new ItemPeersStorage<ItemAutomationPeer>();
+                    
 
                     foreach (UIElement child in childItems)
                     {