Add `FormContext` to `ViewContext`

- start with `FormContext` and classes it needs from legacy world
- FYI `ModelClientValidationRule` came from Web Pages; the rest from MVC

Cleanup and make files compile in new world
- remove `FormContext.GetJsonValidationMetadata` method; will file an
  issue to revive this using Json.NET
- don't store `FormContext` in the `HttpContext`, no longer have child
  actions
- do `null` checks in setters, not getters (minor perf improvement)
- fix namespaces and usings
- wrap long lines; use `[NotNull]`; no copyright notice
- use explicit comparers for dictionaries
- add XML comment for odd `ModelClientValidationRule.ValidationType`
  property
- Collection -> List

src/Microsoft.AspNet.Mvc.ModelBinding/Validation/FieldValidationMetadata.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+
+namespace Microsoft.AspNet.Mvc.ModelBinding
+{
+    public class FieldValidationMetadata
+    {
+        private readonly List<ModelClientValidationRule> _validationRules =
+            new List<ModelClientValidationRule>();
+        private string _fieldName = string.Empty;
+
+        public string FieldName
+        {
+            get { return _fieldName; }
+            set { _fieldName = value ?? string.Empty; }
+        }
+
+        public bool ReplaceValidationMessageContents { get; set; }
+
+        public string ValidationMessageId { get; set; }
+
+        public IList<ModelClientValidationRule> ValidationRules
+        {
+            get { return _validationRules; }
+        }
+    }
+}

src/Microsoft.AspNet.Mvc.ModelBinding/Validation/ModelClientValidationRule.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Collections.Generic;
+
+namespace Microsoft.AspNet.Mvc.ModelBinding
+{
+    public class ModelClientValidationRule
+    {
+        private readonly Dictionary<string, object> _validationParameters =
+            new Dictionary<string, object>(StringComparer.Ordinal);
+        private string _validationType = string.Empty;
+
+        public string ErrorMessage { get; set; }
+
+        public IDictionary<string, object> ValidationParameters
+        {
+            get { return _validationParameters; }
+        }
+
+        /// <summary>
+        /// Identifier of the <see cref="ModelClientValidationRule"/>. If client-side unobtrustive validation is
+        /// enabled, use this <see langref="string"/> as part of the generated "data-val" attribute name. Must be
+        /// unique in the set of enabled validation rules.
+        /// </summary>
+        public string ValidationType
+        {
+            get { return _validationType; }
+            set { _validationType = value ?? string.Empty; }
+        }
+    }
+}

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

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.AspNet.Mvc.ModelBinding;
+
+namespace Microsoft.AspNet.Mvc.Rendering
+{
+    public class FormContext
+    {
+        private readonly Dictionary<string, FieldValidationMetadata> _fieldValidators =
+            new Dictionary<string, FieldValidationMetadata>(StringComparer.Ordinal);
+        private readonly Dictionary<string, bool> _renderedFields =
+            new Dictionary<string, bool>(StringComparer.Ordinal);
+
+        public IDictionary<string, FieldValidationMetadata> FieldValidators
+        {
+            get { return _fieldValidators; }
+        }
+
+        public string FormId { get; set; }
+
+        public bool ReplaceValidationSummary { get; set; }
+
+        public string ValidationSummaryId { get; set; }
+
+        public FieldValidationMetadata GetValidationMetadataForField([NotNull] string fieldName)
+        {
+            return GetValidationMetadataForField(fieldName, createIfNotFound: false);
+        }
+
+        public FieldValidationMetadata GetValidationMetadataForField([NotNull] string fieldName, bool createIfNotFound)
+        {
+            FieldValidationMetadata metadata;
+            if (!FieldValidators.TryGetValue(fieldName, out metadata))
+            {
+                if (createIfNotFound)
+                {
+                    metadata = new FieldValidationMetadata()
+                    {
+                        FieldName = fieldName
+                    };
+                    FieldValidators[fieldName] = metadata;
+                }
+            }
+
+            return metadata;
+        }
+
+        public bool RenderedField([NotNull] string fieldName)
+        {
+            bool result;
+            _renderedFields.TryGetValue(fieldName, out result);
+
+            return result;
+        }
+
+        public void RenderedField([NotNull] string fieldName, bool value)
+        {
+            _renderedFields[fieldName] = value;
+        }
+    }
+}

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

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using Microsoft.AspNet.Abstractions;
@@ -9,15 +9,35 @@ namespace Microsoft.AspNet.Mvc.Rendering
     {
         private DynamicViewData _viewBag;
 
-        public ViewContext(IServiceProvider serviceProvider, HttpContext httpContext, IDictionary<string, object> viewEngineContext)
+        // We need a default FormContext if the user uses html <form> instead of an MvcForm
+        private readonly FormContext _defaultFormContext = new FormContext();
+
+        private FormContext _formContext;
+
+        public ViewContext(IServiceProvider serviceProvider, HttpContext httpContext,
+            IDictionary<string, object> viewEngineContext)
         {
             ServiceProvider = serviceProvider;
             HttpContext = httpContext;
             ViewEngineContext = viewEngineContext;
+            _formContext = _defaultFormContext;
         }
 
         public IViewComponentHelper Component { get; set; }
 
+        public virtual FormContext FormContext
+        {
+            get
+            {
+                return _formContext;
+            }
+            set
+            {
+                // Never return a null form context, this is important for validation purposes.
+                _formContext = value ?? _defaultFormContext;
+            }
+        }
+
         public HttpContext HttpContext { get; private set; }
 
         public IServiceProvider ServiceProvider { get; private set; }