Add a trace event to MemoryPressureListener::NotifyMemoryPressure.

Add a trace event to MemoryPressureListener::NotifyMemoryPressure.

Add a trace event to MemoryPressureListener::NotifyMemoryPressure to enable
tracking of whether any jank is caused by dealing with memory pressure
notifications.

BUG=397026
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=285449

[rmcilroy, 2014-07-24 17:59:07]

Mark, could you please take a look, thanks.

[Mark Mentovai, 2014-07-24 18:00:47]

LGTM

[rmcilroy, 2014-07-24 18:08:40]

The CQ bit was checked by rmcilroy@chromium.org

[commit-bot: I haz the power, 2014-07-24 18:11:44]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rmcilroy@chromium.org/413233002/1

[commit-bot: I haz the power, 2014-07-24 21:48:19]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_chromium_chromeos_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_chrome...)
  linux_chromium_rel_swarming on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_rel_sw...)
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-07-24 22:23:01]

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

[commit-bot: I haz the power, 2014-07-24 22:23:02]

Try jobs failed on following builders:
  linux_chromium_rel_swarming on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_rel_sw...)

[rmcilroy, 2014-07-24 22:27:40]

The CQ bit was checked by rmcilroy@chromium.org

[commit-bot: I haz the power, 2014-07-24 22:29:29]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rmcilroy@chromium.org/413233002/1

[commit-bot: I haz the power, 2014-07-25 01:42:01]

Change committed as 285449