PartitionAlloc: Move PurgeMemory to PartitionRootBase.

This small CL unifies |PurgeMemory()| in PartitionRootBase. Besides making the
decommit code more regular, this will make a common periodic decommit in
base/allocator clearer.

Bug: 942512
Change-Id: I9cab9d9012e87622a09bf22e055278cf16b4f8a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1609701
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Benoit L <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659941}
3 files changed