Add CompressingTreeList.GetRunLength method.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@6074 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Utils/CompressingTreeList.cs

@@ -343,9 +343,20 @@ namespace ICSharpCode.AvalonEdit.Utils
 					n = n.Successor;
 				}
 			}
+			Debug.Assert(index == this.Count);
 			return -1;
 		}
 		
+		/// <summary>
+		/// Gets the number of elements after <paramref name="index"/> that have the same value as each other.
+		/// </summary>
+		public int GetRunLength(int index)
+		{
+			if (index < 0 || index >= this.Count)
+				throw new ArgumentOutOfRangeException("index", index, "Value must be between 0 and " + (this.Count - 1));
+			return GetNode(ref index).count - index;
+		}
+		
 		/// <summary>
 		/// Inserts the specified <paramref name="item"/> at <paramref name="index"/>
 		/// </summary>