Mark FastSharedBufferReader's methods const

Source/platform/image-decoders/FastSharedBufferReader.h

 /*
  * Copyright (C) 2015 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 36 matching lines @@
     FastSharedBufferReader(PassRefPtr<SharedBuffer> data);
 
     void setData(PassRefPtr<SharedBuffer>);
 
     // Returns a consecutive buffer that carries the data starting
     // at |dataPosition| with |length| bytes.
     // This method returns a pointer to a memory segment stored in
     // |m_data| if such a consecutive buffer can be found.
     // Otherwise copies into |buffer| and returns it.
     // Caller must ensure there are enough bytes in |m_data| and |buffer|.
-    const char* getConsecutiveData(size_t dataPosition, size_t length, char* buffer);
+    const char* getConsecutiveData(size_t dataPosition, size_t length, char* buffer) const;
 
     // Wraps SharedBuffer::getSomeData().
-    size_t getSomeData(const char*& someData, size_t dataPosition);
+    size_t getSomeData(const char*& someData, size_t dataPosition) const;
 
     // Returns a byte at |dataPosition|.
     // Caller must ensure there are enough bytes in |m_data|.
-    inline char getOneByte(size_t dataPosition)
+    inline char getOneByte(size_t dataPosition) const
     {
         return *getConsecutiveData(dataPosition, 1, 0);
     }
 
     size_t size() const
     {
         return m_data->size();
     }
 
 private:
-    void getSomeDataInternal(unsigned dataPosition);
+    void getSomeDataInternal(unsigned dataPosition) const;
 
     RefPtr<SharedBuffer> m_data;
 
     // Caches the last segment of |m_data| accessed, since subsequent reads are
     // likely to re-access it.
-    const char* m_segment;
-    size_t m_segmentLength;
+    mutable const char* m_segment;
+    mutable size_t m_segmentLength;
 
     // Data position in |m_data| pointed to by |m_segment|.
-    size_t m_dataPosition;
+    mutable size_t m_dataPosition;
 };
 
 } // namespace blink
 
 #endif