Remove our own ReadOnlyDictionary and update usages

OpenRA.Game/Graphics/ChromeProvider.cs

@@ -52,7 +52,7 @@ namespace OpenRA.Graphics
 			public readonly Dictionary<string, Rectangle> Regions = new Dictionary<string, Rectangle>();
 		}
 
-		public static IReadOnlyDictionary<string, Collection> Collections { get; private set; }
+		public static IReadOnlyDictionary<string, Collection> Collections => collections;
 		static Dictionary<string, Collection> collections;
 		static Dictionary<string, (Sheet Sheet, int Density)> cachedSheets;
 		static Dictionary<string, Dictionary<string, Sprite>> cachedSprites;
@@ -77,8 +77,6 @@ namespace OpenRA.Graphics
 			cachedPanelSprites = new Dictionary<string, Sprite[]>();
 			cachedCollectionSheets = new Dictionary<Collection, (Sheet, int)>();
 
-			Collections = new ReadOnlyDictionary<string, Collection>(collections);
-
 			var chrome = MiniYaml.Merge(modData.Manifest.Chrome
 				.Select(s => MiniYaml.FromStream(fileSystem.Open(s), s)));
 

OpenRA.Game/Graphics/CursorProvider.cs

@@ -38,8 +38,7 @@ namespace OpenRA.Graphics
 			Palettes = nodesDict["Cursors"].Nodes.Select(n => n.Value.Value)
 				.Where(p => p != null)
 				.Distinct()
-				.ToDictionary(p => p, p => pals[p].ReadPalette(modData.DefaultFileSystem))
-				.AsReadOnly();
+				.ToDictionary(p => p, p => pals[p].ReadPalette(modData.DefaultFileSystem));
 
 			var frameCache = new FrameCache(fileSystem, modData.SpriteLoaders);
 			var cursors = new Dictionary<string, CursorSequence>();
@@ -47,7 +46,7 @@ namespace OpenRA.Graphics
 				foreach (var sequence in s.Value.Nodes)
 					cursors.Add(sequence.Key, new CursorSequence(frameCache, sequence.Key, s.Key, s.Value.Value, sequence.Value));
 
-			Cursors = cursors.AsReadOnly();
+			Cursors = cursors;
 		}
 
 		public bool HasCursorSequence(string cursor)

OpenRA.Game/Graphics/HardwarePalette.cs

@@ -28,7 +28,7 @@ namespace OpenRA.Graphics
 		public HardwarePalette()
 		{
 			Texture = Game.Renderer.Context.CreateTexture();
-			readOnlyModifiablePalettes = modifiablePalettes.AsReadOnly();
+			readOnlyModifiablePalettes = modifiablePalettes;
 		}
 
 		public bool Contains(string name)

OpenRA.Game/Graphics/Model.cs

@@ -10,6 +10,7 @@
 #endregion
 
 using System;
+using System.Collections.Generic;
 using OpenRA.FileSystem;
 using OpenRA.Primitives;
 

OpenRA.Game/Graphics/SequenceProvider.cs

@@ -125,7 +125,7 @@ namespace OpenRA.Graphics
 				}
 			}
 
-			return new ReadOnlyDictionary<string, UnitSequences>(items);
+			return items;
 		}
 
 		public void Preload()