Core - Add IRequestContext.GetCookieManagerAsync extension method

- Will return the cookie manager when the backing store has loaded
  otherwise returns null

CefSharp.Test/Framework/RequestContextExtensionFacts.cs

@@ -4,12 +4,15 @@
 
 using System;
 using System.Collections.Generic;
+using System.Threading.Tasks;
 using Moq;
 using Xunit;
 using Xunit.Abstractions;
 
 namespace CefSharp.Test.Framework
 {
+    //NOTE: All Test classes must be part of this collection as it manages the Cef Initialize/Shutdown lifecycle
+    [Collection(CefSharpFixtureCollection.Key)]
     public class RequestContextExtensionFacts
     {
         private const string ProxyPreferenceKey = "proxy";
@@ -70,5 +73,20 @@ public void SetProxyThrowsExceptionOnInvalidScheme()
                 mockRequestContext.Object.SetProxy("myscheme", "localhost", 0, out msg);
             });
         }
+
+        [Fact]
+        public async Task CanGetCookieManagerForRequestContextAsync()
+        {
+            var requestContext = RequestContext
+                .Configure()
+                .Create();
+
+            var cookieManager = await requestContext.GetCookieManagerAsync();
+
+            var cookies = await cookieManager.VisitAllCookiesAsync();
+
+            Assert.NotNull(cookies);
+            output.WriteLine("Cookie Count {0}", cookies.Count);
+        }
     }
 }

CefSharp/RequestContextExtensions.cs

@@ -59,6 +59,29 @@ public static void LoadExtensionsFromDirectory(this IRequestContext requestConte
             }
         }
 
+        /// <summary>
+        /// Gets the cookie manager associated with the <see cref="IRequestContext"/>. Once the cookie manager
+        /// storage has been initialized the method will return.
+        /// </summary>
+        /// <exception cref="Exception">Thrown when an exception error condition occurs.</exception>
+        /// <param name="requestContext">The <see cref="IRequestContext"/> instance this method extends.</param>
+        /// <returns>returns <see cref="ICookieManager"/> if the store was successfully loaded otherwise null. </returns>
+        public static async Task<ICookieManager> GetCookieManagerAsync(this IRequestContext requestContext)
+        {
+            if (requestContext == null)
+            {
+                throw new Exception("RequestContext is null, unable to obtain cookie manager");
+            }
+
+            var callback = new TaskCompletionCallback();
+
+            var cookieManager = requestContext.GetCookieManager(callback);
+
+            var success = await callback.Task;
+
+            return success ? cookieManager : null;
+        }
+
         /// <summary>
         /// Set the value associated with preference name. If value is null the
         /// preference will be restored to its default value. If setting the preference