Trace every incremental marking step.

Trace every incremental marking step.

- This information is required in the chrome trace for a GC telemetry
  benchmark.

R=hpayer@chromium.org, jochen@chromium.org
BUG=

Committed: https://code.google.com/p/v8/source/detail?r=22643

[ernstm, 2014-07-25 12:04:45]

PTAL

[Hannes Payer (out of office), 2014-07-25 18:27:21]

LGTM, if the overhead of this call is negligible

We should also move the histogram timer from AdvanceIdleIncrementalMarking into
this function. I guess the intent was to log every incremental marking step, not
just the steps triggered within the idle notification.

[ernstm, 2014-07-28 08:54:17]

On 2014/07/25 18:27:21, Hannes Payer wrote:
> LGTM, if the overhead of this call is negligible

The overhead is very low, if Chrome tracing is not enabled.

> We should also move the histogram timer from AdvanceIdleIncrementalMarking
into
> this function. I guess the intent was to log every incremental marking step,
not
> just the steps triggered within the idle notification.

We don't need this call at all, if we can move the histogram timer from
AdvanceIdleIncrementalMarking to Step. The histogram timer issues a Chrome trace
event internally. Jochen, can we just move the timer around?

[jochen (gone - plz use gerrit), 2014-07-28 08:54:56]

On 2014/07/28 at 08:54:17, ernstm wrote:
> On 2014/07/25 18:27:21, Hannes Payer wrote:
> > LGTM, if the overhead of this call is negligible
> 
> The overhead is very low, if Chrome tracing is not enabled.
> 
> > We should also move the histogram timer from AdvanceIdleIncrementalMarking
into
> > this function. I guess the intent was to log every incremental marking step,
not
> > just the steps triggered within the idle notification.
> 
> We don't need this call at all, if we can move the histogram timer from
AdvanceIdleIncrementalMarking to Step. The histogram timer issues a Chrome trace
event internally. Jochen, can we just move the timer around?

sure

[ernstm, 2014-07-28 10:43:37]

Moved HistogramTimerScope from Heap::AdvanceIdleIncrementalMarking to
IncrementalMarking::Step. The diff looks bigger, because the added scope around
the timed code and git cl format touched almost every line in Step.

[jochen (gone - plz use gerrit), 2014-07-28 11:17:52]

lgtm

[Hannes Payer (out of office), 2014-07-28 11:17:58]

lgtm

[ernstm, 2014-07-28 12:33:32]

Committed patchset #2 manually as r22643 (presubmit successful).