Bug 1374643: Use IID instead of REFIID for a11y::HandlerProvider::mTargetUnkIid; r=jimm

MozReview-Commit-ID: IMFMxhHsbp6

--HG--
extra : amend_source : 10f8b88b0ba538241b59e88ad145db7479d64c07

accessible/ipc/win/HandlerProvider.h

@@ -64,7 +64,7 @@ private:
 
   Atomic<uint32_t>                  mRefCnt;
   Mutex                             mMutex; // Protects mSerializer
-  REFIID                            mTargetUnkIid;
+  const IID                         mTargetUnkIid;
   mscom::InterceptorTargetPtr<IUnknown> mTargetUnk; // Constant, main thread only
   UniquePtr<mscom::StructToStream>  mSerializer;
 };