Introduce a flag for tracing retaining path in GC.

Introduce a flag for tracing retaining path in GC.

The retaining path is the exactly the path visited by the marker.

Since it adds run-time overhead, it is guarded by a compile flag.

BUG=

[ulan, 2015-02-05 16:08:11]

ulan@chromium.org changed reviewers:
+ hpayer@chromium.org

[ulan, 2015-02-05 16:08:41]

PTAL

[Hannes Payer (out of office), 2015-02-06 13:31:32]

I like the idea a lot. But I am a bit worried about the code pollution.
Additionally to the gc_tracer, we would have to maintain these type of tracing
calls as well. Would it make sense to integrate some of the calls (e.g. for the
roots) in the GCTracer? That would mean we would have to add more GCTracer calls
but at least some of the calls would handle both. Not sure if this is cleaner...
WDYT?

https://codereview.chromium.org/890663005/diff/40001/src/heap/heap.cc
File src/heap/heap.cc (right):

https://codereview.chromium.org/890663005/diff/40001/src/heap/heap.cc#newcode...
src/heap/heap.cc:5610: if (mark_sweeps > 5 && WeakCell::cast(dc->get(i +
1))->value() == obj) {
make 5 a constant

https://codereview.chromium.org/890663005/diff/40001/src/heap/heap.cc#newcode...
src/heap/heap.cc:5625: 
+1 newline