RFR (xs): 8221509: Refactor assert( G1CollectedHeap::used() == recalculate_used() ) with better message

[sangheon.kim at oracle.com]

Hi all,

Can I have some reviews that replace assert(used() == 
recalculated_used()) with better message?
Those assert messages are not much helpful as it doesn't include any 
actual values on it so I'm suggesting to include actual values of each 
and then replace as a macro.

CR: https://bugs.openjdk.java.net/browse/JDK-8221509
webrev: http://cr.openjdk.java.net/~sangheki/8221509/webrev.0/
testing: local build

Thanks,
Sangheon