Add alphaType() to SkImage

src/image/SkImage_Base.h

Index: src/image/SkImage_Base.h
diff --git a/src/image/SkImage_Base.h b/src/image/SkImage_Base.h
index 09971c1198de0333122fa3a9289ce7ba76009549..bfa183d5a93b2e9fd47547544297809fde918804 100644
--- a/src/image/SkImage_Base.h
+++ b/src/image/SkImage_Base.h
@@ -31,6 +31,7 @@ public:
     // Implementors: if you can not return the value, return an invalid ImageInfo with w=0 & h=0
     // & unknown color space.
     virtual SkImageInfo onImageInfo() const = 0;
+    virtual SkAlphaType onAlphaType() const = 0;
 
     virtual bool onPeekPixels(SkPixmap*) const { return false; }