Re-land: base: Introduce an explicit call for reducing emulated discardable memory usage.

Re-land: base: Introduce an explicit call for reducing emulated discardable memory usage.
    
This removes the use of memory pressure signals from discardable memory
system and instead introduces an explicit call for reducing emulated
discardable memory that the renderer can call when all widgets are hidden
until we have a better mechanism in place.
    
BUG=398087
TEST=base_unittests,content_browsertests

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=289127

[reveman, 2014-08-07 15:24:29]

Alternative patch. I'll update the description if this looks good. Removes
memory pressure signals from discardable memory and restricts the temporary
"reduce memory when widget count goes to 0" hack to emulated discardable memory
API.

Please take a look.

https://codereview.chromium.org/448173002/diff/1/base/memory/discardable_memo...
File base/memory/discardable_memory_emulated.h (right):

https://codereview.chromium.org/448173002/diff/1/base/memory/discardable_memo...
base/memory/discardable_memory_emulated.h:28: static void
ReduceMemoryUsageUntilWithinModeratePressureLimit();
Note: I can rename all references to "ModeratePressure" to something else if
preferred? Avoiding it in this initial patchset to first make sure the approach
is OK and it will touch a lot of code so might make the patch a bit harder to
review.

[Mark Mentovai, 2014-08-07 15:30:27]

This design is better.

[reveman, 2014-08-08 08:23:17]

I've update the patch. I think this is ready to land. PTAL.

[jochen (gone - plz use gerrit), 2014-08-11 14:33:00]

content/ lgtm

[Mark Mentovai, 2014-08-11 14:51:19]

LGTM

[reveman, 2014-08-11 15:35:48]

The CQ bit was checked by reveman@chromium.org

[commit-bot: I haz the power, 2014-08-11 15:37:16]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/reveman@chromium.org/448173002/20001

[commit-bot: I haz the power, 2014-08-11 17:44:24]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/40077)
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)
  mac_chromium_compile_dbg on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  mac_chromium_rel_swarming on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[commit-bot: I haz the power, 2014-08-11 17:47:19]

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

[commit-bot: I haz the power, 2014-08-11 17:47:20]

Try jobs failed on following builders:
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)

[reveman, 2014-08-11 17:56:58]

The CQ bit was checked by reveman@chromium.org

[commit-bot: I haz the power, 2014-08-11 17:57:50]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/reveman@chromium.org/448173002/40001

[commit-bot: I haz the power, 2014-08-11 21:09:43]

Change committed as 288793

[tapted, 2014-08-12 03:53:01]

A revert of this CL has been created in
https://codereview.chromium.org/458343003/ by tapted@chromium.org.

The reason for reverting is: tree-closer ui_unittests failing on Linux Chromium
OS ASan LSan Tests (1)
test
RenderThreadImplBrowserTest.EmulatedDiscardableMemoryDiscardedWhenWidgetsHidden
failing since
http://build.chromium.org/p/chromium.memory/builders/Linux%20Chromium%20OS%20...

Error: LeakSanitizer: detected memory leaks (Various Indirect leaks).
..
SUMMARY: AddressSanitizer: 19178 byte(s) leaked in 34 allocation(s)..

[reveman, 2014-08-12 16:13:12]

FYI, I'm going to re-land this with
EmulatedDiscardableMemoryDiscardedWhenWidgetsHidden test disabled when using
lsan as it turned out to be a bit complicated to fix this without major changes.
It's important to land this fix asap and leaks as part of the unit test is not a
blocker imo. Other RenderThreadImplBrowser tests are already disabled with
lsan..

[reveman, 2014-08-12 16:13:20]

The CQ bit was checked by reveman@chromium.org

[commit-bot: I haz the power, 2014-08-12 16:14:31]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/reveman@chromium.org/448173002/80001

[commit-bot: I haz the power, 2014-08-12 20:49:10]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[commit-bot: I haz the power, 2014-08-13 00:06:55]

Change committed as 289127