Shrink trace_event buffers

Shrink trace_event buffers

The original 500000 is way too big. Shrink non-ring-buffer by 1/2
and ring-buffer to 1/4 of non-ring-buffer.

Tests showed that for a busy app with impl-side-painting enabled,
the shrunk ring buffer can contain about 3-5 seconds of trace.
The time will double after we switch to X event for B/E events.

BUG=248022
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=218119

[dsinclair, 2013-08-16 19:04:41]

Do we want to reduce the non-ring buffer size as well? We're going to hit memory
issues in both cases with impl-side painting I think.

[Xianzhu, 2013-08-16 19:17:50]

On 2013/08/16 19:04:41, dsinclair wrote:
> Do we want to reduce the non-ring buffer size as well? We're going to hit
memory
> issues in both cases with impl-side painting I think.

For non-ring buffer, I think we can keep as-is. The user can stop the tracing
earlier to avoid OOM. Another user having a machine with more memory and/or
tracing fewer processes may want to get longer traces.

For ring buffer, we should avoid OOM as much as possible as the buffer is more
likely to be full.

[nduca, 2013-08-16 19:31:02]

LGTM but lets reduce the non-ring-buffer by 1/2 just because its way too big
right now.

[Xianzhu, 2013-08-16 19:47:13]

On 2013/08/16 19:31:02, nduca wrote:
> LGTM but lets reduce the non-ring-buffer by 1/2 just because its way too big
> right now.

Done. Now shrink both.

[commit-bot: I haz the power, 2013-08-16 19:58:24]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/22796009/4002

[commit-bot: I haz the power, 2013-08-16 23:26:09]

Change committed as 218119