Reduce the number of worker threads GN uses.

Reduce the number of worker threads GN uses.

I noticed the main thread is being starved which slows down execution. On a Z620 using the new default improves generation speed for Chrome by 20%.

This also adds trace events for the OnResolved step of target resolution which is a bottleneck in some cases.

Committed: https://crrev.com/d0f8e7b23cd48a8e4685e82b7beffb0930554bba
Cr-Commit-Position: refs/heads/master@{#360955}

[brettw, 2015-11-19 21:34:28]

brettw@chromium.org changed reviewers:
+ cpu@chromium.org

[brettw, 2015-11-19 21:34:32]

The CQ bit was checked by brettw@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-11-19 21:38:47]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1464463003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1464463003/1

[commit-bot: I haz the power, 2015-11-19 23:45:40]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-11-19 23:45:41]

Dry run: Try jobs failed on following builders:
  ios_dbg_simulator_ninja on tryserver.chromium.mac (JOB_TIMED_OUT, no build
URL)
  ios_rel_device_ninja on tryserver.chromium.mac (JOB_TIMED_OUT, no build URL)

[brettw, 2015-11-20 00:02:57]

The CQ bit was checked by brettw@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-11-20 00:06:36]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1464463003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1464463003/1

[commit-bot: I haz the power, 2015-11-20 00:39:39]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-11-20 00:39:40]

Dry run: This issue passed the CQ dry run.

[cpu_(ooo_6.6-7.5), 2015-11-20 22:25:59]

lgtm

[brettw, 2015-11-20 23:01:47]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-11-20 23:05:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1464463003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1464463003/1

[commit-bot: I haz the power, 2015-11-20 23:52:43]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-20 23:53:32]

Patchset 1 (id:??) landed as
https://crrev.com/d0f8e7b23cd48a8e4685e82b7beffb0930554bba
Cr-Commit-Position: refs/heads/master@{#360955}