Fix For Bug#507240 Marshal.IsComObject fails for __ComObject in x-plat MCG

Yi/Alan/Tyler found out this bug and the root cause--- IsComObject(Type t) only check whether t is subclass of __ComObject or not --- IsSubclassOf fails if type is exactly __ComObject: https://msdn.microsoft.com/en-us/library/system.type.issubclassof%28v=vs.110%29.aspx

the fix is to add a check to see whether type itself  is __ComObject or not.

Changes:
1. Unify IsCOMObject and IsComObject into IsComObject. don't confuse ourselves
2. Move McgComHelpers.IsComObject into McgMarshal.IsComObject

TODO:
1. Consider to split McgMarshal.cs into McgMarshal.Pinvoke.cs/McgMarshal.Com.cs/McgMarshal.WinRT.cs/McgMarshal.Common.cs

[tfs-changeset: 1678276]

4 files changed, 21 insertions, 20 deletions

diff --git a/src/System.Private.Interop/src/Shared/McgComHelpers.cs b/src/System.Private.Interop/src/Shared/McgComHelpers.cs
index 781232011..603543449 100644
--- a/src/System.Private.Interop/src/Shared/McgComHelpers.cs
+++ b/src/System.Private.Interop/src/Shared/McgComHelpers.cs
@@ -231,14 +231,6 @@ namespace System.Runtime.InteropServices
         }
 
         /// <summary>
-        /// Return true if the object is a RCW. False otherwise
-        /// </summary>
-        internal static bool IsComObject(object obj)
-        {
-            return (obj is __ComObject);
-        }
-
-        /// <summary>
         /// Unwrap if this is a managed wrapper
         /// Typically used in data binding
         /// For example, you don't want to data bind against a KeyValuePairImpl<K, V> - you want the real 
diff --git a/src/System.Private.Interop/src/Shared/McgMarshal.cs b/src/System.Private.Interop/src/Shared/McgMarshal.cs
index 2c3b9e5a4..b9db11146 100644
--- a/src/System.Private.Interop/src/Shared/McgMarshal.cs
+++ b/src/System.Private.Interop/src/Shared/McgMarshal.cs
@@ -78,15 +78,26 @@ namespace System.Runtime.InteropServices
 #endif
         }
 
-        public static bool IsCOMObject(Type type)
+        /// <summary>
+        /// Return true if the type is __COM or derived from __COM. False otherwise
+        /// </summary>
+        public static bool IsComObject(Type type)
         {
 #if RHTESTCL
             return false;
 #else
-            return type.GetTypeInfo().IsSubclassOf(typeof(__ComObject));
+            return type == typeof(__ComObject) || type.GetTypeInfo().IsSubclassOf(typeof(__ComObject));
 #endif
         }
 
+        /// <summary>
+        /// Return true if the object is a RCW. False otherwise
+        /// </summary>
+        internal static bool IsComObject(object obj)
+        {
+            return (obj is __ComObject);
+        }
+
         public static T FastCast<T>(object value) where T : class
         {
             // We have an assert here, to verify that a "real" cast would have succeeded.
@@ -401,7 +412,7 @@ namespace System.Runtime.InteropServices
 
 #endregion
 
-#region COM marshalling
+        #region COM marshalling
 
         /// <summary>
         /// Explicit AddRef for RCWs
@@ -921,10 +932,9 @@ namespace System.Runtime.InteropServices
         {
             return CoCreateInstanceEx(clsid, string.Empty);
         }
+        #endregion
 
-#endregion
-
-#region Testing
+        #region Testing
 
         /// <summary>
         /// Internal-only method to allow testing of apartment teardown code
@@ -1063,7 +1073,7 @@ namespace System.Runtime.InteropServices
 
             IntPtr pResult = default(IntPtr);
 
-            int hr = CalliIntrinsics.StdCall<int>(
+            int hr = CalliIntrinsics.StdCall__int(
                 pIActivationFactoryInternal->pVtable->pfnActivateInstance,
                 pIActivationFactoryInternal,
                 &pResult
diff --git a/src/System.Private.Interop/src/System/Runtime/InteropServices/Marshal.cs b/src/System.Private.Interop/src/System/Runtime/InteropServices/Marshal.cs
index 28a956b6d..20b088a7a 100644
--- a/src/System.Private.Interop/src/System/Runtime/InteropServices/Marshal.cs
+++ b/src/System.Private.Interop/src/System/Runtime/InteropServices/Marshal.cs
@@ -802,7 +802,7 @@ namespace System.Runtime.InteropServices
             if (o == null)
                 throw new ArgumentNullException(nameof(o), SR.Arg_InvalidHandle);
 
-            return McgComHelpers.IsComObject(o);
+            return McgMarshal.IsComObject(o);
         }
 
         public static unsafe IntPtr StringToCoTaskMemUni(String s)
diff --git a/src/System.Private.Interop/src/System/Runtime/InteropServices/MarshalImpl.cs b/src/System.Private.Interop/src/System/Runtime/InteropServices/MarshalImpl.cs
index 973b305a7..20f08a919 100644
--- a/src/System.Private.Interop/src/System/Runtime/InteropServices/MarshalImpl.cs
+++ b/src/System.Private.Interop/src/System/Runtime/InteropServices/MarshalImpl.cs
@@ -38,18 +38,18 @@ namespace System.Runtime.InteropServices
         {
             if (o == null)
                 throw new ArgumentNullException(nameof(o));
-            return McgMarshal.IsCOMObject(o.GetType());
+            return McgMarshal.IsComObject(o);
         }
         public static int ReleaseComObject(object o)
         {
             if (o == null)
                 throw new ArgumentNullException(nameof(o));
-            return McgMarshal.Release(o as __ComObject);            
+            return McgMarshal.Release(o as __ComObject);
         }
 
         public static int FinalReleaseComObject(object o)
         {
-            return McgMarshal.FinalReleaseComObject(o);          
+            return McgMarshal.FinalReleaseComObject(o);
         }
 
         public static int QueryInterface(IntPtr pUnk, ref Guid iid, out IntPtr ppv)
@@ -72,6 +72,5 @@ namespace System.Runtime.InteropServices
         {
             return McgMarshal.ComRelease(pUnk);
         }
-
     }
 }