Oilpan: The number of normal persistent handles shouldn't be used for estimating heap size

Oilpan: The number of normal persistent handles shouldn't be used for estimating heap size

Currently we're estimating the live heap size as follows:

  (live heap size) = (current heap size) - ((heap size at last GC) / (# of persistent handles at last GC) * (# of persistent handles collected since last GC))

In this equation, "persistent handles" contains V8 wrappers and normal persistent handles.
This CL drops the normal persistent handles from the "persistent handles".

The reason is that it doesn't make much sense to take into account the number of normal persistent handles
because normal persistent handles can frequently be allocated and deallocated on stack.
Those on-stack persistent handles can even be nullptr. It doesn't make sense to assume that
these persistent handles are holding a substantial amount of memory.

I've sometimes observed that conservative GCs get scheduled a bit too aggressively
because the memory held by the persistent handles is overestimated. This CL fixes the issue.

BUG=474470
Committed: https://crrev.com/2a9913f8f4cd3a9c343fbf0ef074dd466b2b80ca
git-svn-id: svn://svn.chromium.org/blink/trunk@202104 bbb929c8-8fbe-4397-9dbb-9b2b20218538

[haraken, 2015-09-10 13:03:12]

haraken@chromium.org changed reviewers:
+ keishi@chromium.org, yutak@chromium.org

[haraken, 2015-09-10 13:03:33]

PTAL

I'll collect full memory numbers on memory.top_7_stress overnight.

[haraken, 2015-09-11 00:17:57]

On 2015/09/10 13:03:33, haraken wrote:
> PTAL
> 
> I'll collect full memory numbers on memory.top_7_stress overnight.

I observed no memory increase in memory.top_7_stress with this CL.

PTAL.

[keishi, 2015-09-11 02:44:17]

LGTM

[haraken, 2015-09-11 03:26:10]

The CQ bit was checked by haraken@chromium.org

[commit-bot: I haz the power, 2015-09-11 03:26:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335493003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335493003/20001

[commit-bot: I haz the power, 2015-09-11 04:12:50]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=202104

[commit-bot: I haz the power, 2015-09-23 12:18:47]

Patchset 2 (id:??) landed as
https://crrev.com/2a9913f8f4cd3a9c343fbf0ef074dd466b2b80ca