Add luminance mask transfer modes.

gm/xfermodes.cpp

Index: gm/xfermodes.cpp
diff --git a/gm/xfermodes.cpp b/gm/xfermodes.cpp
index 65f53bffe703ac56a16b1e161f2073600259de52..0cd1a29f45d132ba7ec06e2d1a97a4cbe0ad20f5 100644
--- a/gm/xfermodes.cpp
+++ b/gm/xfermodes.cpp
@@ -78,7 +78,7 @@ protected:
     }
 
     virtual SkISize onISize() {
-        return make_isize(790, 640);
+        return make_isize(790, 680);
     }
 
     virtual void onDraw(SkCanvas* canvas) {
@@ -118,6 +118,8 @@ protected:
             { SkXfermode::kSaturation_Mode,   "Saturation"    },
             { SkXfermode::kColor_Mode,        "Color"         },
             { SkXfermode::kLuminosity_Mode,   "Luminosity"    },
+            { SkXfermode::kSrcInLum_Mode,     "SrcInLum"      },
+            { SkXfermode::kDstInLum_Mode,     "DstInLum"      },
         };
 
         const SkScalar w = SkIntToScalar(W);