include: Add definition of MilMatrix3x2D.

include/dwmapi.h

diff --git a/include/dwmapi.h b/include/dwmapi.h
index 551138e..4fe51bc 100644
--- a/include/dwmapi.h
+++ b/include/dwmapi.h
@@ -31,6 +31,16 @@
 
 DECLARE_HANDLE(HTHUMBNAIL);
 
+typedef struct _MilMatrix3x2D
+{
+    DOUBLE S_11;
+    DOUBLE S_12;
+    DOUBLE S_21;
+    DOUBLE S_22;
+    DOUBLE DX;
+    DOUBLE DY;
+} MilMatrix3x2D;
+
 DWMAPI DwmEnableComposition(UINT);
 DWMAPI DwmEnableMMCSS(BOOL);
 DWMAPI DwmExtendFrameIntoClientArea(HWND,const MARGINS*);