BIND 10 #2572: extend MasterLexer to provide current/total bytes of source(s)

[BIND 10 Development]

#2572: extend MasterLexer to provide current/total bytes of source(s)
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                   Reporter:         |                 Owner:  UnAssigned
  jinmei                             |                Status:  new
                       Type:  task   |             Milestone:  New Tasks
                   Priority:         |              Keywords:
  medium                             |             Sensitive:  0
                  Component:         |           Sub-Project:  DNS
  libdns++                           |  Estimated Difficulty:  0
               CVSS Scoring:         |           Total Hours:  0
            Defect Severity:  N/A    |
Feature Depending on Ticket:         |
  loadzone-ng                        |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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 We need additional interfaces to `MasterLexer` to show the progress
 of zone loading in percentage (just like the old b10-loadzone did):
 - return the total byte count of the entire source(s)
 - return the current position of the lexer in the source(s) in bytes

 Note that `MasterLexer` may have pushed other sources.  The intent
 of this interface is the sum of all the sources, and the sum of
 the position counts of all the sources (otherwise the progress can be
 misleading especially in such cases as a small top most zone file
 includes a large one).

 Note also that the source may be a stream object, in which case it's
 not feasible to return the actual "total byte count".  We'll need some
 special value to represent it (a conceptual "infinite" or something).

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Ticket URL: <http://bind10.isc.org/ticket/2572>
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BIND 10 Development