Add IRequiredMemberSelector support in NetCore assembly

Author: dougbu

src/System.Net.Http.Formatting/Formatting/MediaTypeFormatter.cs

@@ -129,7 +129,6 @@ internal List<MediaTypeMapping> MediaTypeMappingsInternal
             get { return _mediaTypeMappings; }
         }
 
-#if !NETFX_CORE // IRequiredMemberSelector is not in portable libraries because there is no model state on the client.
         /// <summary>
         /// Gets or sets the <see cref="IRequiredMemberSelector"/> used to determine required members.
         /// </summary>
@@ -144,7 +143,6 @@ public virtual IRequiredMemberSelector RequiredMemberSelector
                 _requiredMemberSelector = value;
             }
         }
-#endif
 
         internal virtual bool CanWriteAnyTypes
         {

test/System.Net.Http.Formatting.Test/Formatting/JsonNetValidationTest.cs

@@ -43,7 +43,6 @@ public static TheoryDataSet<string, Type, int> Theories
             }
         }
 
-#if !NETFX_CORE // IRequiredMemeberSelector is not in portable libraries because there is no model state on the client.
         [Theory]
         [PropertyData("Theories")]
         public async Task ModelErrorsPopulatedWithValidationErrors(string json, Type type, int expectedErrors)
@@ -56,7 +55,6 @@ public async Task ModelErrorsPopulatedWithValidationErrors(string json, Type typ
 
             mockLogger.Verify(mock => mock.LogError(It.IsAny<string>(), It.IsAny<Exception>()), Times.Exactly(expectedErrors));
         }
-#endif
 
         [Fact]
         public async Task HittingMaxDepthRaisesOnlyOneValidationError()
@@ -81,7 +79,6 @@ public async Task HittingMaxDepthRaisesOnlyOneValidationError()
         }
     }
 
-#if !NETFX_CORE // IRequiredMemeberSelector is not in portable libraries because there is no model state on the client.
     // this IRMS treats all member names that start with "Required" as required
     public class SimpleRequiredMemberSelector : IRequiredMemberSelector
     {
@@ -90,7 +87,6 @@ public bool IsRequiredMember(MemberInfo member)
             return member.Name.StartsWith("Required");
         }
     }
-#endif
 
     public class DataContractWithRequiredMembers
     {