This CL adds client.toDataURL which gets the contents...

core/cross/bitmap.cc

 /*
  * Copyright 2009, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 128 matching lines @@
   unsigned mip_height = image::ComputeMipDimension(level, height());
   DCHECK(dst_left + src_width <= mip_width &&
          dst_top + src_height <= mip_height);
   bool compressed = Texture::IsCompressedFormat(format());
   bool entire_rect = dst_left == 0 && dst_top == 0 &&
                      src_width == mip_width && src_height == mip_height;
   DCHECK(!compressed || entire_rect);
 
   uint8* dst =
       GetMipData(level) +
-      image::ComputeMipChainSize(mip_width, dst_top, format(), 1) +
-      image::ComputeMipChainSize(dst_left, 1, format(), 1);
+      image::ComputePitch(format(), mip_width) * dst_top +
+      image::ComputePitch(format(), dst_left);
 
   const uint8* src = static_cast<const uint8*>(src_data);
   if (!compressed) {
     unsigned bytes_per_line = image::ComputePitch(format(), src_width);
     int dst_pitch = image::ComputePitch(format(), mip_width);
     for (unsigned yy = 0; yy < src_height; ++yy) {
       memcpy(dst, src, bytes_per_line);
       src += src_pitch;
       dst += dst_pitch;
     }
@@ skipping 398 matching lines @@
       return false;
   }
   return true;
 }
 
 ObjectBase::Ref Bitmap::Create(ServiceLocator* service_locator) {
   return ObjectBase::Ref(new Bitmap(service_locator));
 }
 
 }  // namespace o3d