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]

1 files changed, 1 insertions, 1 deletions

diff --git a/src/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.Interop.cs b/src/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.Interop.cs
index 0fb7029d9..a8f668627 100644
--- a/src/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.Interop.cs
+++ b/src/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.Interop.cs
@@ -16,7 +16,7 @@ namespace Internal.Reflection.Execution
     {
         public sealed override bool IsCOMObject(Type type)
         {
-            return McgMarshal.IsCOMObject(type);
+            return McgMarshal.IsComObject(type);
         }
     }
 }