Remove SkEncodedInfo kUnknown_Color and kUnknown_Alpha from public API

src/codec/SkJpegDecoderMgr.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkJpegDecoderMgr_DEFINED
 #define SkJpegDecoderMgr_DEFINED
 
@@ skipping 25 matching lines @@
      */
     JpegDecoderMgr(SkStream* stream);
 
     /*
      * Initialize decompress struct
      * Initialize the source manager
      */
     void  init();
 
     /*
-     * Returns the encoded color type of the jpeg, or kUnknown if the
-     * color type can't be determined
+     * Returns true if it successfully sets outColor to the encoded color,
+     * and false otherwise.
      */
-    SkEncodedInfo::Color getEncodedColor();
+    bool getEncodedColor(SkEncodedInfo::Color* outColor);
 
     /*
      * Free memory used by the decode manager
      */
     ~JpegDecoderMgr();
 
     /*
      * Get the jump buffer in order to set an error return point
      */
     jmp_buf& getJmpBuf();
 
     /*
      * Get function for the decompress info struct
      */
     jpeg_decompress_struct* dinfo();
 
 private:
 
     jpeg_decompress_struct fDInfo;
     skjpeg_source_mgr      fSrcMgr;
     skjpeg_error_mgr       fErrorMgr;
     bool                   fInit;
 };
 
 #endif