[iOS] Fix child view position when the Navigation Bar is translucent (#659)

Xamarin.Forms.Platform.iOS/Renderers/NavigationRenderer.cs

@@ -154,7 +154,7 @@ namespace Xamarin.Forms.Platform.iOS
 
 			var toolbar = _secondaryToolbar;
 			// Use 0 if the NavBar is hidden or will be hidden
-			var toolbarY = NavigationBarHidden || !NavigationPage.GetHasNavigationBar(Current) ? 0 : navBarFrame.Bottom;
+			var toolbarY = NavigationBarHidden || NavigationBar.Translucent || !NavigationPage.GetHasNavigationBar(Current) ? 0 : navBarFrame.Bottom;
 			toolbar.Frame = new RectangleF(0, toolbarY, View.Frame.Width, toolbar.Frame.Height);
 
 			double trueBottom = toolbar.Hidden ? toolbarY : toolbar.Frame.Bottom;
@@ -824,7 +824,13 @@ namespace Xamarin.Forms.Platform.iOS
 			public override void ViewWillAppear(bool animated)
 			{
 				UpdateNavigationBarVisibility(animated);
-				EdgesForExtendedLayout = UIRectEdge.None;
+
+				NavigationRenderer n;
+				var isTranslucent = false;
+				if (_navigation.TryGetTarget(out n))
+					isTranslucent = n.NavigationBar.Translucent;
+				EdgesForExtendedLayout = isTranslucent ? UIRectEdge.All : UIRectEdge.None;
+
 				base.ViewWillAppear(animated);
 			}