Move DM png code to picture_utils, for use by other tools.

tools/picture_utils.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef picture_utils_DEFINED
 #define picture_utils_DEFINED
 
-class SkBitmap;
+#include "SkBitmap.h"
+
+class SkData;
 class SkString;
 
 namespace sk_tools {
     // since PNG insists on unpremultiplying our alpha, we take no precision
     // chances and force all pixels to be 100% opaque, otherwise on compare we
     // may not get a perfect match.
     //
     // This expects a bitmap with a config type of 8888 and for the pixels to
     // not be on the GPU.
     void force_all_opaque(const SkBitmap& bitmap);
@@ skipping 18 matching lines @@
      * @param bm the bitmap to record
      * @param dirPath directory within which to write the image file
      * @param subdirOrNull subdirectory within dirPath, or nullptr to just write into dirPath
      * @param baseName last part of the filename
      *
      * @return true if written out successfully
      */
     bool write_bitmap_to_disk(const SkBitmap& bm, const SkString& dirPath,
                               const char *subdirOrNull, const SkString& baseName);
 
+    // Return raw unpremultiplied RGBA bytes, suitable for storing in a PNG. The output
+    // colors are assumed to be sRGB values. This is only guaranteed to work for the
+    // cases that are currently emitted by tools:
+    // Linear premul 8888, sRGB premul 8888, Linear premul F16
+    sk_sp<SkData> encode_bitmap_for_png(SkBitmap bitmap);
+
 } // namespace sk_tools
 
 #endif  // picture_utils_DEFINED