Benchmarks for IndentingPrintWriter.

Current timings on a mako listed below, which show minimal overhead
compared to writing directly. The increased code readability and
automatic indenting is worth the overhead.

Also worth noting is that writing concatenated strings is
substantially faster than printing components separately.

           benchmark      us linear runtime
       ComplexDirect 10712.7 =========================
    ComplexIndenting 12623.7 ==============================
       PairIndenting    45.8 =
             PairRaw    82.1 =
        SimpleDirect   282.2 =
     SimpleIndenting   294.4 =

Change-Id: I7c38690c14b017fa46248ebb0be69f6beff03371