Revert of base: Introduce an explicit call for reducing emulated discardable memory usage.

Revert of base: Introduce an explicit call for reducing emulated discardable memory usage. (https://codereview.chromium.org/448173002/)

Reason for revert:
tree-closer content_browsertests 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%20ASan%20LSan%20Tests%20%281%29/builds/2501

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

Original issue's description:
> 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=288793

TBR=jochen@chromium.org,mark@chromium.org,reveman@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=398087
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=288913

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

Created Revert of base: Introduce an explicit call for reducing emulated
discardable memory usage.

[commit-bot: I haz the power, 2014-08-12 03:54:52]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/tapted@chromium.org/458343003/1

[commit-bot: I haz the power, 2014-08-12 03:56:45]

Change committed as 288913