Add experimental support for tracing the state of the VM heap to a file

Add experimental support for tracing the state of the VM heap to a file
or socket.

[Vyacheslav Egorov (Chromium), 2011-09-28 15:21:11]

it kinda lgtm

but I would prefer that we have a nice interface for it instead of writing loops
over visualizers directly in many different places. 

To keep changes contained/isolated/compact we should just call different hooks
from different places (spaces{-inl,}.{cc,h}) without looping over visualizers
every time. Take a look at how it is done for GDBJIT or profiler.

This would guarantee that our low-level files do not depend on visualizer
internals.

http://codereview.chromium.org/8055029/diff/1/src/spaces.cc
File src/spaces.cc (right):

http://codereview.chromium.org/8055029/diff/1/src/spaces.cc#newcode447
src/spaces.cc:447: if (owner != NULL) {
Move out of the spaces.cc to some visualizer specific place and keep only a call
to this function here.

Just to keep things isolated with a small interface like we do with GDBJIT or
profiler.

http://codereview.chromium.org/8055029/diff/1/src/spaces.cc#newcode483
src/spaces.cc:483: vis != NULL;
ditto

http://codereview.chromium.org/8055029/diff/1/src/spaces.cc#newcode940
src/spaces.cc:940: !page->is_anchor();
ditto

http://codereview.chromium.org/8055029/diff/1/src/spaces.h
File src/spaces.h (right):

http://codereview.chromium.org/8055029/diff/1/src/spaces.h#newcode1361
src/spaces.h:1361: FreeListNode* get_chain(int i) {
make enum!