Made some work towards DI compatibility.

Little refactorings, the OutputCacheManager(OutputCacheProvider outputCacheProvider, IKeyBuilder keyBuilder) ctor is now public.
The DonutOutputCacheAttribute has now two public constructors.

Author: moonpyk

DevTrends.MvcDonutCaching/DonutOutputCacheAttribute.cs

@@ -19,10 +19,10 @@ public class DonutOutputCacheAttribute : ActionFilterAttribute, IExceptionFilter
         private bool? _noStore;
         private OutputCacheOptions? _options;
 
-        public DonutOutputCacheAttribute()
-        {
-            var keyBuilder = new KeyBuilder();
+        public DonutOutputCacheAttribute() : this(new KeyBuilder()) { }
 
+        public DonutOutputCacheAttribute(IKeyBuilder keyBuilder)
+        {
             _keyGenerator         = new KeyGenerator(keyBuilder);
             _outputCacheManager   = new OutputCacheManager(OutputCache.Instance, keyBuilder);
             _donutHoleFiller      = new DonutHoleFiller(new EncryptingActionSettingsSerialiser(new ActionSettingsSerialiser(), new Encryptor()));

DevTrends.MvcDonutCaching/OutputCacheManager.cs

@@ -12,13 +12,11 @@ public class OutputCacheManager : IExtendedOutputCacheManager
         private readonly OutputCacheProvider _outputCacheProvider;
         private readonly IKeyBuilder _keyBuilder;
 
-        public OutputCacheManager()
+        public OutputCacheManager() : this(OutputCache.Instance, new KeyBuilder())
         {
-            _outputCacheProvider = OutputCache.Instance;
-            _keyBuilder = new KeyBuilder();
         }
 
-        internal OutputCacheManager(OutputCacheProvider outputCacheProvider, IKeyBuilder keyBuilder)
+        public OutputCacheManager(OutputCacheProvider outputCacheProvider, IKeyBuilder keyBuilder)
         {
             _outputCacheProvider = outputCacheProvider;
             _keyBuilder = keyBuilder;