Ported changes from #1417 to PullRequestFilesView.

Author: grokys

src/GitHub.VisualStudio/Views/GitHubPane/PullRequestFilesView.xaml

@@ -40,6 +40,7 @@
               BorderThickness="0"
               Margin="0 6 0 0"
               ContextMenuOpening="changesTree_ContextMenuOpening"
+              KeyUp="changesTree_KeyUp"
               MouseDoubleClick="changesTree_MouseDoubleClick"
               MouseRightButtonDown="changesTree_MouseRightButtonDown">
         <TreeView.ItemContainerStyle>
@@ -57,7 +58,9 @@
             </HierarchicalDataTemplate>
 
             <DataTemplate DataType="{x:Type vm:PullRequestFileNode}">
-                <StackPanel Orientation="Horizontal" Tag="{Binding DataContext, ElementName=root}">
+                <StackPanel Orientation="Horizontal"
+                            Tag="{Binding DataContext, ElementName=root}"
+                            KeyboardNavigation.DirectionalNavigation="None">
 
                     <!-- 
                       We need to change the color of the file icon when the file is deleted, but applying the style

src/GitHub.VisualStudio/Views/GitHubPane/PullRequestFilesView.xaml.cs

@@ -32,7 +32,7 @@ void changesTree_ContextMenuOpening(object sender, ContextMenuEventArgs e)
         void changesTree_MouseDoubleClick(object sender, MouseButtonEventArgs e)
         {
             var file = (e.OriginalSource as FrameworkElement)?.DataContext as IPullRequestFileNode;
-            (DataContext as IPullRequestFilesViewModel)?.DiffFile.Execute(file);            
+            (DataContext as IPullRequestFilesViewModel)?.DiffFile.Execute(file);
         }
 
         void changesTree_MouseRightButtonDown(object sender, MouseButtonEventArgs e)
@@ -70,5 +70,18 @@ void ApplyContextMenuBinding<TItem>(object sender, ContextMenuEventArgs e) where
                 }
             }
         }
+
+        private void changesTree_KeyUp(object sender, KeyEventArgs e)
+        {
+            if (e.Key == Key.Return)
+            {
+                var file = (e.OriginalSource as FrameworkElement)?.DataContext as IPullRequestFileNode;
+
+                if (file != null)
+                {
+                    (DataContext as IPullRequestFilesViewModel)?.DiffFile.Execute(file);
+                }
+            }
+        }
     }
 }