Revert of Re-land: base: Enable browser-wide discardable memory on Linux, CrOS and Windows.

Revert of Re-land: base: Enable browser-wide discardable memory on Linux, CrOS and Windows. (patchset #1 id:1 of https://codereview.chromium.org/793443003/)

Reason for revert:
Need to fix these issues before reland:
crbug.com/450096
crbug.com/450122
crbug.com/449907

Original issue's description:
> Re-land: base: Enable browser-wide discardable memory on Linux, CrOS and Windows.
>
> This makes SHMEM implementation of discardable memory preferred
> over EMULATED implementation. This effectively makes SHMEM the
> implementation used by default on Linux, CrOS and Windows.
>
> SHMEM implementation of discardable memory gives the browser
> process control over the total amount of discardable memory used
> and allows us to enforce a global limit of 512MB across all
> renderers.
>
> BUG=429415, 429416
>
> Committed: https://crrev.com/07e0fd329293cca145875e156b87afdf383dcdc0
> Cr-Commit-Position: refs/heads/master@{#312045}

TBR=avi@chromium.org,danakj@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=429415, 429416
Committed: https://crrev.com/1374d88a7d60d1ad80adcfd038ca4a9b83d0c627
Cr-Commit-Position: refs/heads/master@{#312214}

[reveman, 2015-01-20 17:12:59]

Created Revert of Re-land: base: Enable browser-wide discardable memory on
Linux, CrOS and Windows.

[commit-bot: I haz the power, 2015-01-20 17:13:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/808743004/1

[commit-bot: I haz the power, 2015-01-20 17:14:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-20 17:15:23]

Patchset 1 (id:??) landed as
https://crrev.com/1374d88a7d60d1ad80adcfd038ca4a9b83d0c627
Cr-Commit-Position: refs/heads/master@{#312214}