RFR: 8144732: VM_HeapDumper hits assert with bad dump_len

[Andreas Eriksson]

Hi,

Please review this fix for dumping of long arrays.

Bug:
8144732: VM_HeapDumper hits assert with bad dump_len
https://bugs.openjdk.java.net/browse/JDK-8144732

Webrev:
http://cr.openjdk.java.net/~aeriksso/8144732/webrev.00/

Problem:
The hprof format uses an u4 as a record length field, but arrays can be 
longer than that (counted in bytes).

Fix:
Truncate the dump length of the array using a new function, 
calculate_array_max_length. For a given array it returns the number of 
elements we can dump. That length is then used to truncate arrays that 
are too long.
Whenever an array is truncated a warning is printed:
Java HotSpot(TM) 64-Bit Server VM warning: cannot dump array of type 
object[] with length 1,073,741,823; truncating to length 536,870,908

Much of the change is moving functions needed by 
calculate_array_max_length to the DumpWriter or DumperSupport class so 
that they can be accessed.

Regards,
Andreas