Add SkBitmap::readPixels() and reimplement copyTo and SkCanvas::readPixels

include/core/SkBitmap.h

Index: include/core/SkBitmap.h
diff --git a/include/core/SkBitmap.h b/include/core/SkBitmap.h
index 51e9a9243a13b156ab8591d888b79bbbd11588e6..541db79bb3741a9e3dcdc3ba22dbe2089d6e8096 100644
--- a/include/core/SkBitmap.h
+++ b/include/core/SkBitmap.h
@@ -591,6 +591,28 @@ public:
     }
 
     /**
+     *  Copy the bitmap's pixels into the specified buffer (pixels + rowBytes),
+     *  converting them into the requested format (SkImageInfo). The src pixels are read
+     *  starting at the specified (srcX,srcY) offset, relative to the top-left corner.
+     *
+     *  The specified ImageInfo and (srcX,srcY) offset specifies a source rectangle
+     *
+     *      srcR.setXYWH(srcX, srcY, dstInfo.width(), dstInfo.height());
+     *
+     *  srcR is intersected with the bounds of the bitmap. If this intersection is not empty,
+     *  then we have two sets of pixels (of equal size). Replace the dst pixels with the
+     *  corresponding src pixels, performing any colortype/alphatype transformations needed
+     *  (in the case where the src and dst have different colortypes or alphatypes).
+     *
+     *  This call can fail, returning false, for several reasons:
+     *  - If srcR does not intersect the bitmap bounds.
+     *  - If the requested colortype/alphatype cannot be converted from the src's types.
+     *  - If the src pixels are not available.
+     */
+    bool readPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRowBytes,
+                    int srcX, int srcY) const;
+
+    /**
      *  Returns true if this bitmap's pixels can be converted into the requested
      *  colorType, such that copyTo() could succeed.
      */