Support for "Do not blend" in mux and demux libraries

Change-Id: I9566a8e2d059fe1ebd9ca99c7e13311bf3f8f281

examples/webpmux.c

@@ -430,6 +430,8 @@ static int ParseFrameArgs(const char* args, WebPMuxFrameInfo* const info) {
   // Note: The sanity of the following conversion is checked by
   // WebPMuxSetAnimationParams().
   info->dispose_method = (WebPMuxAnimDispose)dispose_method;
+  // TODO(urvang): Add support for parsing blending method too.
+  info->blend_method = WEBP_MUX_BLEND;
   return 1;
 }