[WP8] fix memory leak when Resume game

ContentManager & ContentReaders was creating new instances during
AssetReload. The problem was with SoundEffectReader, VertexBufferReader
and generally with Shared resources like VertexBuffer, IndexBuffer,
Effect.

The problem was previously reported here:
MonoGame#1771

http://community.monogame.net/t/sharpdx-crashing-the-app-after-having-resumed-a-few-times/813/10

Tested on WP8.

MonoGame.Framework/Content/ContentReader.cs

@@ -44,6 +44,7 @@ public sealed class ContentReader : BinaryReader
         private ContentTypeReader[] typeReaders;
 		internal int version;
 		internal int sharedResourceCount;
+        Dictionary<int, object> sharedResources;
 
         internal ContentTypeReader[] TypeReaders
         {
@@ -105,6 +106,7 @@ internal void InitializeTypeReaders()
             typeReaderManager = new ContentTypeReaderManager();
             typeReaders = typeReaderManager.LoadAssetReaders(this);
             sharedResourceCount = Read7BitEncodedInt();
+            sharedResources = new Dictionary<int, object>(sharedResourceCount);
             sharedResourceFixups = new List<KeyValuePair<int, Action<object>>>();
         }
 
@@ -120,9 +122,18 @@ internal void ReadSharedResources()
                 if (index > 0)
                 {
                     ContentTypeReader contentReader = typeReaders[index - 1];
+                    int resourceId = i + 1;
+                    if (!this.sharedResources.ContainsKey(resourceId))
+                    {                        
                     sharedResources[i] = ReadObject<object>(contentReader);
                 }
                 else
+                {
+                        object existingInstance = this.sharedResources[resourceId];
+                        sharedResources[i] = contentReader.Read(this, existingInstance);
+                    }
+                }
+                else
                 {
                     sharedResources[i] = null;
                 }
@@ -281,6 +292,27 @@ public void ReadSharedResource<T>(Action<T> fixup)
             }
         }
 
+        public void ReadSharedResource<T>(Action<T> fixup, T existingInstance)
+        {
+            int index = Read7BitEncodedInt();
+            if (index > 0)
+            {
+                sharedResourceFixups.Add(new KeyValuePair<int, Action<object>>(index - 1, delegate(object v)
+                {
+                    if (!(v is T))
+                    {
+                        throw new ContentLoadException(String.Format("Error loading shared resource. Expected type {0}, received type {1}", typeof(T).Name, v.GetType().Name));
+                    }
+                    fixup((T)v);
+                }));
+                if (existingInstance != null)
+                {
+                    if (!sharedResources.ContainsKey(index))
+                        sharedResources.Add(index, existingInstance);
+                }
+            }
+        }
+
         public Vector2 ReadVector2()
         {
             Vector2 result = new Vector2();

MonoGame.Framework/Content/ContentReaders/EffectReader.cs

@@ -31,11 +31,17 @@ private static bool Contains(string search, string[] arr)
 
         protected internal override Effect Read(ContentReader input, Effect existingInstance)
         {
-            int count = input.ReadInt32();
+            Effect effect = existingInstance;
 
-            var effect = new Effect(input.GraphicsDevice,input.ReadBytes(count));
-            effect.Name = input.AssetName;
+            var dataCount = (int)input.ReadUInt32();
+            var data = input.ReadBytes(dataCount);
+
+            if (effect == null)
+            {
+                effect = new Effect(input.GraphicsDevice, data);
+            }            
 
+            effect.Name = input.AssetName;            
             return effect;
         }
     }

MonoGame.Framework/Content/ContentReaders/SoundEffectReader.cs

@@ -109,6 +109,11 @@ protected internal override SoundEffect Read(ContentReader input, SoundEffect ex
             else
                 throw new NotSupportedException("Unsupported wave format!");
 
+            if(existingInstance!=null)
+            {
+                return existingInstance;
+            }
+
             return new SoundEffect(data, 0, count, sampleRate, (AudioChannels)channels, loopStart, loopLength)
             {
                 _format = waveFormat,

MonoGame.Framework/Content/ContentReaders/VertexBufferReader.cs

@@ -34,13 +34,19 @@ class VertexBufferReader : ContentTypeReader<VertexBuffer>
     {
         protected internal override VertexBuffer Read(ContentReader input, VertexBuffer existingInstance)
         {
+            VertexBuffer vertexBuffer = existingInstance;
+
             var declaration = input.ReadRawObject<VertexDeclaration>();
             var vertexCount = (int)input.ReadUInt32();
             var data = input.ReadBytes(vertexCount * declaration.VertexStride);
 
-            var buffer = new VertexBuffer( input.GraphicsDevice, declaration, vertexCount, BufferUsage.None );
-            buffer.SetData( data );
-            return buffer;
+            if(vertexBuffer == null)
+            { 
+                vertexBuffer = new VertexBuffer(input.GraphicsDevice, declaration, vertexCount, BufferUsage.None);
+            }
+
+            vertexBuffer.SetData( data );
+            return vertexBuffer;
         }
     }
 }