Add `TemplateInfo` property to `ViewDataDictionary`

Compared to legacy MVC:
- correct usings and namespace
- remove `GetFullHtmlFieldId` method; depends on `HtmlHelper` method that
  can't be static
- String -> string
- remove reference to a legacy bug
- convert internal `VisitedObjects` property to public `AddVisited()` method

Further cleanup
- remove explicit backing fields for remaining properties
- add copy constructor to replace code distributed around legacy MVC
- don't "combine and trim" in `GetFullHtmlFieldName()`

src/Microsoft.AspNet.Mvc.Rendering/View/TemplateInfo.cs

@@ -0,0 +1,67 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.AspNet.Mvc.ModelBinding;
+
+namespace Microsoft.AspNet.Mvc.Rendering
+{
+    public class TemplateInfo
+    {
+        // Keep a collection of visited objects to prevent infinite recursion.
+        private HashSet<object> _visitedObjects;
+
+        public TemplateInfo()
+        {
+            FormattedModelValue = string.Empty;
+            HtmlFieldPrefix = string.Empty;
+            _visitedObjects = new HashSet<object>();
+        }
+
+        public TemplateInfo(TemplateInfo original)
+        {
+            FormattedModelValue = original.FormattedModelValue;
+            HtmlFieldPrefix = original.HtmlFieldPrefix;
+            _visitedObjects = new HashSet<object>(original._visitedObjects);
+        }
+
+        public object FormattedModelValue { get; set; }
+
+        public string HtmlFieldPrefix { get; set; }
+
+        public int TemplateDepth
+        {
+            get { return _visitedObjects.Count; }
+        }
+
+        public bool AddVisited(object value)
+        {
+            return _visitedObjects.Add(value);
+        }
+
+        public string GetFullHtmlFieldName(string partialFieldName)
+        {
+            if (string.IsNullOrEmpty(partialFieldName))
+            {
+                return HtmlFieldPrefix;
+            }
+            else if (string.IsNullOrEmpty(HtmlFieldPrefix))
+            {
+                return partialFieldName;
+            }
+            else if (partialFieldName.StartsWith("[", StringComparison.Ordinal))
+            {
+                // The partialFieldName might represent an indexer access, in which case combining
+                // with a 'dot' would be invalid.
+                return HtmlFieldPrefix + partialFieldName;
+            }
+            else
+            {
+                return HtmlFieldPrefix + "." + partialFieldName;
+            }
+        }
+
+        public bool Visited(ModelMetadata metadata)
+        {
+            return _visitedObjects.Contains(metadata.Model ?? metadata.ModelType);
+        }
+    }
+}

src/Microsoft.AspNet.Mvc.Rendering/View/ViewDataDictionary.cs

@@ -21,6 +21,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
             [NotNull] ModelStateDictionary modelState)
         {
             ModelState = modelState;
+            TemplateInfo = new TemplateInfo();
             _data = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
             _metadataProvider = metadataProvider;
         }
@@ -41,6 +42,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
             : this(source.MetadataProvider)
         {
             _modelMetadata = source.ModelMetadata;
+             TemplateInfo = new TemplateInfo(source.TemplateInfo);
 
             foreach (var entry in source.ModelState)
             {
@@ -75,6 +77,8 @@ namespace Microsoft.AspNet.Mvc.Rendering
             }
         }
 
+        public TemplateInfo TemplateInfo { get; private set; }
+
         /// <summary>
         /// Provider for subclasses that need it to override <see cref="ModelMetadata"/>.
         /// </summary>