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:
Seems to be causing crashes: https://crash/browse?q=product.name%3D%27Chrome%27%20AND%20product.version%3D%2741.0.2271.0%27%20AND%20custom_data.ChromeCrashProto.ptype%3D%27renderer%27

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/fdfea459b1e5b3ffae10b781a33f884b99a0f2a4
> Cr-Commit-Position: refs/heads/master@{#310628}

TBR=avi@chromium.org,reveman@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=429415, 429416
Committed: https://crrev.com/5521f0c581ca363d6134265913045d21ab81ca0b
Cr-Commit-Position: refs/heads/master@{#310909}

[danakj, 2015-01-10 00:17:21]

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

[commit-bot: I haz the power, 2015-01-10 00:18:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/843153003/1

[commit-bot: I haz the power, 2015-01-10 00:20:01]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-10 00:24:12]

Patchset 1 (id:??) landed as
https://crrev.com/5521f0c581ca363d6134265913045d21ab81ca0b
Cr-Commit-Position: refs/heads/master@{#310909}