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
Review URL: https://codereview.chromium.org/1413163006
Cr-Commit-Position: refs/heads/master@{#355585}
4 files changed
