The default heap ordering is to return the greatest element in the
heap. Since the handle allocator expects a minimal return value on
a new allocation, this caused a bug. The bug is triggered by reserving
handles, allocating new handles, then freeing the handles and
allocating again with the same allocator. Fix the bug by using
std::greater instead of std::less, which will make the heap
return the smallest value instead of largest.

Also adds some logging debugging code for the handle allocators.

Bug: angleproject:1458
Change-Id: Ibef5dcbed0a664ccad0e0335f081e2355162584b
Reviewed-on: https://chromium-review.googlesource.com/848644
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>