RFR(S): 7178846: IterateThroughHeap: heap_iteration_callback passes a negative size for big array

[Staffan Larsen]

Please review the following fix.

Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7178846
Webrev: http://cr.openjdk.java.net/~sla/7178846/webrev.01/

Class CallbackWrapper in jvmtiTagMap.cpp has a missing cast which leads to an 
integer overflow.

The code in question is
    _obj_size = _o->size() * wordSize;

_obj_size is a jlong
_o->size() is an int
wordSize is an int

Changing to:
    _obj_size = (jlong)_o->size() * wordSize;

fixes the overflow.

Thanks,
/Staffan