Re-land: base: Fix registering of memory pressure listeners used when emulating discardable memory.

Re-land: base: Fix registering of memory pressure listeners used when emulating discardable memory.

Memory pressure listeners need to be created on a thread with a message
loop current. Discardable memory is often used on worker threads that
don't have a message loop and with the current system where listeners
are registered on first use, the result is that we're most likely never
notified of memory pressure.

This adds a function to the discardable memory interface that allows us
to register memory pressure listeners on a thread, and at a time, when
we know a message loop is current.

BUG=332570
TBR=jamesr@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=244641

[reveman, 2014-01-09 00:29:19]

Please take a look.

[reveman, 2014-01-10 06:44:38]

Latest patch requires memory pressure listener to be registered and adds a
DCHECK to ensure that this is the case.

The unregister function is needed for proper unit test support where the message
loop needs to change.

PTAL.

[willchan no longer on Chromium, 2014-01-10 07:01:02]

lgtm

[commit-bot: I haz the power, 2014-01-10 18:03:35]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/reveman@chromium.org/129963002/30001

[commit-bot: I haz the power, 2014-01-10 20:18:40]

Change committed as 244229

[reveman, 2014-01-13 18:22:27]

https://codereview.chromium.org/129963002/diff/510001/base/memory/discardable...
File base/memory/discardable_memory_provider.cc (right):

https://codereview.chromium.org/129963002/diff/510001/base/memory/discardable...
base/memory/discardable_memory_provider.cc:75: //
DCHECK(memory_pressure_listener_);
Disabled this DCHECK for now as it's causing webkit_unit_tests to fail. I will
re-enable this as soon as I've added the necessary APIs to blink and skia that
allow us to enforce this everywhere.

[willchan no longer on Chromium, 2014-01-13 18:23:19]

OK

[commit-bot: I haz the power, 2014-01-13 18:25:16]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/reveman@chromium.org/129963002/510001

[commit-bot: I haz the power, 2014-01-13 23:26:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/reveman@chromium.org/129963002/510001

[commit-bot: I haz the power, 2014-01-14 03:09:29]

Change committed as 244641