The extensions require isolate address to be set but don't rely on calling
any runtime functions, which makes them viable for post-mortem debugging,
if the corresponding memory is included into the dump

!set_iso(isolate_address)
    call this function before using !mem or other heap routines

!mem or !mem(\"space1[ space2 ...]\")
    prints memory chunks from the 'space' owned by the heap in the
    isolate set by !set_iso; valid values for 'space' are:
    new, old, map, code, lo [large], nlo [newlarge], ro [readonly]
    if no 'space' specified prints memory chunks for all spaces,
    e.g. !mem(\"code\"), !mem(\"ro new old\")

!where(address)
    prints name of the space and address of the MemoryChunk the
    'address' is from, e.g. !where(0x235cb869f9)


Output from !mem would look something like this:

0:000> !mem("old")
Heap at 0x210652b8838
Im   address:	 object area start - end (size)
OldSpace (allocating at: 0x1703dae7a20):
*    0x33d9a8c0000:	 0x33d9a8c0138 - 0x33d9a8f1000 (0x31000)
     0x1703dac0000:	 0x1703dac0138 - 0x1703db00000 (0x40000)

Change-Id: Iae1a217bbc5c5a88e2cf742db88ead9bb6fc904c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1669744
Commit-Queue: Irina Yatsenko <irinayat@microsoft.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62316}