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..af33cb261517258d7d88900bec47d1a33507f7f0 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 +131,8 @@ public:
     */
     int rowBytesAsPixels() const { return fRowBytes >> (fBytesPerPixel >> 1); }
 
+    SkAlphaType alphaType() const { return (SkAlphaType)fAlphaType; }
+
     /** Return the address of the pixels for this SkBitmap.
     */
     void* getPixels() const { return fPixels; }
@@ -248,7 +251,14 @@ 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 +682,7 @@ private:
     uint32_t    fWidth;
     uint32_t    fHeight;
     uint8_t     fConfig;
+    uint8_t     fAlphaType;

[scroggo, 2013/09/30 19:01:28]

This should be serialized, and we should bump the PICTURE_VERSION (I'm fine to
do it later for convenience/grouping, but the code should at least be there
behind a flag).

     uint8_t     fFlags;
     uint8_t     fBytesPerPixel; // based on config