Revert of base: Use MADV_REMOVE instead of ftruncate to purge discardable memory segments.

Revert of base: Use MADV_REMOVE instead of ftruncate to purge discardable memory segments. (patchset #11 id:190001 of https://codereview.chromium.org/1409743002/ )

Reason for revert:
Causing crashes on MacOSX: crbug.com/546642

Original issue's description:
> base: Use MADV_REMOVE instead of ftruncate to purge discardable memory segments.
>
> This makes the discardable memory implementation use
> madvise(MADV_REMOVE) to tell the kernel to free resources
> associated with purged pages. This cleans up the code as
> madvise - unlike ftruncate - doesn't require us to keep the
> file descriptor open and it has the huge advantage that
> discardable memory can be shared between a renderer and
> the GPU process.
>
> This also works with Ashmem for which ftrunctate is not
> supported.
>
> BUG=543633
> TEST=base_unittests --gtest_filter=DiscardableSharedMemoryTest.ZeroFilledPagesAfterPurge
>
> Committed: https://crrev.com/dc9010e6a83e6cc0e424d482fe038d4b1c889f60
> Cr-Commit-Position: refs/heads/master@{#355391}

TBR=avi@chromium.org,danakj@chromium.org,primiano@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=543633, 546642
Committed: https://crrev.com/fbbaf63100f5b57104ecf721e5d2ac4a6319b5bc
Cr-Commit-Position: refs/heads/master@{#355585}

[reveman, 2015-10-22 18:12:38]

Created Revert of base: Use MADV_REMOVE instead of ftruncate to purge
discardable memory segments.

[reveman, 2015-10-22 18:13:01]

Description was changed from

==========
Revert of base: Use MADV_REMOVE instead of ftruncate to purge discardable memory
segments. (patchset #11 id:190001 of https://codereview.chromium.org/1409743002/
)

Reason for revert:
Causing crashes on MacOSX: crbug.com/546642

Original issue's description:
> base: Use MADV_REMOVE instead of ftruncate to purge discardable memory
segments.
> 
> This makes the discardable memory implementation use
> madvise(MADV_REMOVE) to tell the kernel to free resources
> associated with purged pages. This cleans up the code as
> madvise - unlike ftruncate - doesn't require us to keep the
> file descriptor open and it has the huge advantage that
> discardable memory can be shared between a renderer and
> the GPU process.
> 
> This also works with Ashmem for which ftrunctate is not
> supported.
> 
> BUG=543633
> TEST=base_unittests
--gtest_filter=DiscardableSharedMemoryTest.ZeroFilledPagesAfterPurge
> 
> Committed: https://crrev.com/dc9010e6a83e6cc0e424d482fe038d4b1c889f60
> Cr-Commit-Position: refs/heads/master@{#355391}

TBR=avi@chromium.org,danakj@chromium.org,primiano@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=543633
==========

to

==========
Revert of base: Use MADV_REMOVE instead of ftruncate to purge discardable memory
segments. (patchset #11 id:190001 of https://codereview.chromium.org/1409743002/
)

Reason for revert:
Causing crashes on MacOSX: crbug.com/546642

Original issue's description:
> base: Use MADV_REMOVE instead of ftruncate to purge discardable memory
segments.
> 
> This makes the discardable memory implementation use
> madvise(MADV_REMOVE) to tell the kernel to free resources
> associated with purged pages. This cleans up the code as
> madvise - unlike ftruncate - doesn't require us to keep the
> file descriptor open and it has the huge advantage that
> discardable memory can be shared between a renderer and
> the GPU process.
> 
> This also works with Ashmem for which ftrunctate is not
> supported.
> 
> BUG=543633
> TEST=base_unittests
--gtest_filter=DiscardableSharedMemoryTest.ZeroFilledPagesAfterPurge
> 
> Committed: https://crrev.com/dc9010e6a83e6cc0e424d482fe038d4b1c889f60
> Cr-Commit-Position: refs/heads/master@{#355391}

TBR=avi@chromium.org,danakj@chromium.org,primiano@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=543633,546642
==========

[commit-bot: I haz the power, 2015-10-22 18:13:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1413163006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1413163006/1

[commit-bot: I haz the power, 2015-10-22 18:15:35]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-22 18:16:34]

Patchset 1 (id:??) landed as
https://crrev.com/fbbaf63100f5b57104ecf721e5d2ac4a6319b5bc
Cr-Commit-Position: refs/heads/master@{#355585}