don't draw unpremul alpha (yet)

src/core/SkSpriteBlitter_RGB16.cpp

Index: src/core/SkSpriteBlitter_RGB16.cpp
diff --git a/src/core/SkSpriteBlitter_RGB16.cpp b/src/core/SkSpriteBlitter_RGB16.cpp
index 1ba3ee22fcbaae8a4271963f6c3844c7317e6721..3d1d28d0a570dff72b5f26998104f1b024d751c2 100644
--- a/src/core/SkSpriteBlitter_RGB16.cpp
+++ b/src/core/SkSpriteBlitter_RGB16.cpp
@@ -321,15 +321,23 @@ SkSpriteBlitter* SkSpriteBlitter::ChooseD16(const SkBitmap& source, const SkPain
         return NULL;
     }
 
+    const SkAlphaType at = source.alphaType();
+
     SkSpriteBlitter* blitter = NULL;
     unsigned alpha = paint.getAlpha();
 
     switch (source.colorType()) {
         case kN32_SkColorType: {
+            if (kPremul_SkAlphaType != at && kOpaque_SkAlphaType != at) {
+                break;
+            }
             blitter = allocator->createT<Sprite_D16_S32_BlitRowProc>(source);
             break;
         }
         case kARGB_4444_SkColorType:
+            if (kPremul_SkAlphaType != at && kOpaque_SkAlphaType != at) {
+                break;
+            }
             if (255 == alpha) {
                 blitter = allocator->createT<Sprite_D16_S4444_Opaque>(source);
             } else {
@@ -344,6 +352,9 @@ SkSpriteBlitter* SkSpriteBlitter::ChooseD16(const SkBitmap& source, const SkPain
             }
             break;
         case kIndex_8_SkColorType:
+            if (kPremul_SkAlphaType != at && kOpaque_SkAlphaType != at) {
+                break;
+            }
             if (paint.isDither()) {
                 // we don't support dither yet in these special cases
                 break;