Implement scoped_const_refptr template.

webrtc/modules/rtp_rtcp/source/forward_error_correction.h

Index: webrtc/modules/rtp_rtcp/source/forward_error_correction.h
diff --git a/webrtc/modules/rtp_rtcp/source/forward_error_correction.h b/webrtc/modules/rtp_rtcp/source/forward_error_correction.h
index cbeb97e7b1d2876212ca88baae5b6513752e5d96..e16736b3b7130016c7096253fd8f207472508794 100644
--- a/webrtc/modules/rtp_rtcp/source/forward_error_correction.h
+++ b/webrtc/modules/rtp_rtcp/source/forward_error_correction.h
@@ -43,17 +43,17 @@ class ForwardErrorCorrection {
     virtual ~Packet() {}
 
     // Add a reference.
-    virtual int32_t AddRef();
+    virtual int32_t AddRef() const;
 
     // Release a reference. Will delete the object if the reference count
     // reaches zero.
-    virtual int32_t Release();
+    virtual int32_t Release() const;
 
     size_t length;               // Length of packet in bytes.
     uint8_t data[IP_PACKET_SIZE];  // Packet data.
 
    private:
-    int32_t ref_count_;  // Counts the number of references to a packet.
+    mutable int32_t ref_count_;  // Counts the number of references to a packet.
   };
 
   // TODO(holmer): Refactor into a proper class.