Oilpan: Don't call didV8GC in V8's minor GC

Oilpan: Don't call didV8GC in V8's minor GC

didV8GC is used to notify Oilpan that a V8 GC runs and a lot of wrappers
would have been disposed. This is a useful signal for Oilpan to decrease
the estimated live object count. Specifically, Oilpan halves the estimated
live object count when didV8GC is called.

Currently didV8GC is called in both minor and major GCs. This is too much
because minor GCs are called very frequently. As a result, the estimated
live object count goes down too quickly and we end up with scheduling
idle GCs too much.

This CL changes didV8GC so that it is called only in major GCs.

BUG=420515
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196400

[haraken, 2015-06-03 09:41:32]

haraken@chromium.org changed reviewers:
+ oilpan-reviews@chromium.org, sigbjornf@opera.com

[haraken, 2015-06-03 09:41:32]

PTAL

[sof, 2015-06-03 12:04:09]

lgtm, what effect does the slower decay of "estimated object size" have?

[haraken, 2015-06-03 12:10:54]

> what effect does the slower decay of "estimated object size" have?

It will delay both idle and conservative GCs. If the delay becomes a problem, I
think a right fix would be to reduce the 400% to a more modest value.

Currently when we open a Google Search page and search something in oilpan
builds, 8 idle GCs are scheduled in one second -- which looks too many. (We
haven't studied the frequency of idle GCs until today because they rarely run in
benchmarks...)

[haraken, 2015-06-03 12:10:59]

The CQ bit was checked by haraken@chromium.org

[commit-bot: I haz the power, 2015-06-03 12:11:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1161903004/1

[commit-bot: I haz the power, 2015-06-03 14:00:59]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196400