store SkAlphaType inside SkBitmap, on road to support unpremul

include/core/SkBitmap.h

Index: include/core/SkBitmap.h
diff --git a/include/core/SkBitmap.h b/include/core/SkBitmap.h
index 887169ccb522c2820c8c2f0ff3f78e454d0d00cf..5f6fd651c6782613578cccc9e0d1f8cb6e806a02 100644
--- a/include/core/SkBitmap.h
+++ b/include/core/SkBitmap.h
@@ -11,6 +11,7 @@
 #define SkBitmap_DEFINED
 
 #include "Sk64.h"
+#include "SkAlpha.h"
 #include "SkColor.h"
 #include "SkColorTable.h"
 #include "SkPoint.h"
@@ -130,6 +131,9 @@ public:
     */
     int rowBytesAsPixels() const { return fRowBytes >> (fBytesPerPixel >> 1); }
 
+    SkAlphaType alphaType() const { return (SkAlphaType)fAlphaType; }
+    void setAlphaType(SkAlphaType);
+
     /** Return the address of the pixels for this SkBitmap.
     */
     void* getPixels() const { return fPixels; }
@@ -180,7 +184,7 @@ public:
     /** Specify if this bitmap's pixels are all opaque or not. Is only meaningful for configs
         that support per-pixel alpha (RGB32, A1, A8).
     */
-    void setIsOpaque(bool);
+//    void setIsOpaque(bool);
 
     /** Returns true if the bitmap is volatile (i.e. should not be cached by devices.)
     */
@@ -232,13 +236,6 @@ public:
     static bool ComputeIsOpaque(const SkBitmap&);
 
     /**
-     *  Calls ComputeIsOpaque, and passes its result to setIsOpaque().
-     */
-    void computeAndSetOpaquePredicate() {
-        this->setIsOpaque(ComputeIsOpaque(*this));
-    }
-
-    /**
      *  Return the bitmap's bounds [0, 0, width, height] as an SkRect
      */
     void getBounds(SkRect* bounds) const;
@@ -248,7 +245,14 @@ public:
         ComputeRowBytes() is called to compute the optimal value. This resets
         any pixel/colortable ownership, just like reset().
     */
-    void setConfig(Config, int width, int height, size_t rowBytes = 0);
+    bool setConfig(Config, int width, int height, size_t rowBytes, SkAlphaType);
+
+    bool setConfig(Config config, int width, int height, size_t rowBytes = 0) {
+        return this->setConfig(config, width, height, rowBytes,
+                               kPremul_SkAlphaType);
+    }
+
+
     /** Use this to assign a new pixel address for an existing bitmap. This
         will automatically release any pixelref previously installed. Only call
         this if you are handling ownership/lifetime of the pixel memory.
@@ -672,6 +676,7 @@ private:
     uint32_t    fWidth;
     uint32_t    fHeight;
     uint8_t     fConfig;
+    uint8_t     fAlphaType;
     uint8_t     fFlags;
     uint8_t     fBytesPerPixel; // based on config