Make SkSHA1 and SkM5 use common SkDigestHash result type

src/utils/SkBitmapTransformer.h

Index: src/utils/SkBitmapTransformer.h
===================================================================
--- src/utils/SkBitmapTransformer.h	(revision 8826)
+++ src/utils/SkBitmapTransformer.h	(working copy)
@@ -62,6 +62,13 @@
     bool isValid(bool logReason=false) const;
 
     /**
+     * Returns the number of rows in the bitmap.
+     */
+    int numRows() const {
+        return fBitmap.height();
+    }
+
+    /**
      * Returns the number of bytes needed to store a single row of the
      * bitmap's pixels if converted to pixelFormat.
      */
@@ -96,6 +103,22 @@
      */
     bool copyBitmapToPixelBuffer (void *dstBuffer, size_t dstBufferSize) const;
 
+    /**
+     * Writes a single row of the bitmap into dstBuffer, using the
+     * already-specified pixelFormat. Returns true if successful.
+     *
+     * row is the 0-indexed row number within the bitmap; if the row
+     * specified is outside of the range [0, numRows()-1], then this method
+     * will fail.
+     *
+     * dstBufferSize is the maximum allowable bytes to write into dstBuffer;
+     * if that is not large enough to hold the row, then this
+     * will fail immediately and return false.
+     * We force the caller to pass this in to avoid buffer overruns in
+     * unanticipated cases.
+     */
+    bool copyRowToPixelBuffer (int row, void *dstBuffer, size_t dstBufferSize) const;
+
 private:
     const SkBitmap& fBitmap;
     const PixelFormat fPixelFormat;