tdf#38837 Reduce power consumption by minimizing idle timers

Based on profiling, Writer's most CPU consuming idle event was
document statistics calculation.
This patch stops the idle timer once statistics has been updated.
Subsequent profiling shows a sharp decline in CPU usage.

Modifications to the document should initiate statistics update.

Change-Id: I8c38ad8847987264549945e4f482ea18d2635283
Reviewed-on: https://gerrit.libreoffice.org/14575Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>

sw/source/core/doc/DocumentStatisticsManager.cxx

@@ -119,6 +119,8 @@ void DocumentStatisticsManager::UpdateDocStat( bool bCompleteAsync, bool bFields
         }
         else if (IncrementalDocStatCalculate(5000, bFields))
             maStatsUpdateTimer.Start();
+        else
+            maStatsUpdateTimer.Stop();
     }
 }
 
@@ -219,7 +221,7 @@ bool DocumentStatisticsManager::IncrementalDocStatCalculate(long nChars, bool bF
         pType->UpdateFlds();
     }
 
-    return nChars <= 0;
+    return nChars < 0;
 }
 
 IMPL_LINK( DocumentStatisticsManager, DoIdleStatsUpdate, Timer *, pTimer )