store SkAlphaType inside SkBitmap, on road to support unpremul

bench/BitmapScaleBench.cpp

Index: bench/BitmapScaleBench.cpp
diff --git a/bench/BitmapScaleBench.cpp b/bench/BitmapScaleBench.cpp
index cc2a33a894944eee279214c94d86412c47df10ec..ae3df71c22da5c4648415e4b3b8d3bcf146374a3 100644
--- a/bench/BitmapScaleBench.cpp
+++ b/bench/BitmapScaleBench.cpp
@@ -57,14 +57,14 @@ protected:
     }
 
     virtual void onPreDraw() {
-        fInputBitmap.setConfig(SkBitmap::kARGB_8888_Config, fInputSize, fInputSize);
+        fInputBitmap.setConfig(SkBitmap::kARGB_8888_Config,
+                               fInputSize, fInputSize, 0, kOpaque_SkAlphaType);
         fInputBitmap.allocPixels();
         fInputBitmap.eraseColor(SK_ColorWHITE);
-        fInputBitmap.setIsOpaque(true);
 
-        fOutputBitmap.setConfig(SkBitmap::kARGB_8888_Config, fOutputSize, fOutputSize);
+        fOutputBitmap.setConfig(SkBitmap::kARGB_8888_Config,
+                                fOutputSize, fOutputSize, 0, kOpaque_SkAlphaType);
         fOutputBitmap.allocPixels();
-        fOutputBitmap.setIsOpaque(true);
 
         fMatrix.setScale( scale(), scale() );
     }