[C] Add cornerRadius validation, docs

Xamarin.Forms.Core/Frame.cs

@@ -11,7 +11,9 @@ namespace Xamarin.Forms
 
 		public static readonly BindableProperty HasShadowProperty = BindableProperty.Create("HasShadow", typeof(bool), typeof(Frame), true);
 
-		public static readonly BindableProperty CornerRadiusProperty = BindableProperty.Create(nameof(CornerRadius), typeof(float), typeof(Frame), -1.0f);
+		public static readonly BindableProperty CornerRadiusProperty =
+			BindableProperty.Create(nameof(CornerRadius), typeof(float), typeof(Frame), -1.0f,
+									validateValue: (bindable, value) => ((float)value) == -1.0f || ((float)value) >= 0f);
 
 		readonly Lazy<PlatformConfigurationRegistry<Frame>> _platformConfigurationRegistry;
 

docs/Xamarin.Forms.Core/Xamarin.Forms/Frame.xml

@@ -91,6 +91,37 @@ MainPage = new ContentPage () {
         <remarks>A Frame has a default <see cref="P:Xamarin.Forms.Layout.Padding" /> of 20.</remarks>
       </Docs>
     </Member>
+    <Member MemberName="CornerRadius">
+      <MemberSignature Language="C#" Value="public float CornerRadius { get; set; }" />
+      <MemberSignature Language="ILAsm" Value=".property instance float32 CornerRadius" />
+      <MemberType>Property</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>System.Single</ReturnType>
+      </ReturnValue>
+      <Docs>
+        <summary>To be added.</summary>
+        <value>To be added.</value>
+        <remarks>To be added.</remarks>
+      </Docs>
+    </Member>
+    <Member MemberName="CornerRadiusProperty">
+      <MemberSignature Language="C#" Value="public static readonly Xamarin.Forms.BindableProperty CornerRadiusProperty;" />
+      <MemberSignature Language="ILAsm" Value=".field public static initonly class Xamarin.Forms.BindableProperty CornerRadiusProperty" />
+      <MemberType>Field</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>Xamarin.Forms.BindableProperty</ReturnType>
+      </ReturnValue>
+      <Docs>
+        <summary>To be added.</summary>
+        <remarks>To be added.</remarks>
+      </Docs>
+    </Member>
     <Member MemberName="HasShadow">
       <MemberSignature Language="C#" Value="public bool HasShadow { get; set; }" />
       <MemberSignature Language="ILAsm" Value=".property instance bool HasShadow" />