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This adds a system property for controlling unprivileged access to
perf_event_paranoid. It depends on adding kernel support for
perf_event_paranoid=3 based on grsecurity's PERF_HARDEN feature to
completely disable unprivileged access to perf. A minimal port of this
feature is used in the vanilla Debian kernel by default.

It hides the non-hardened value as an implementation detail, since while
it is currently 1, it will probably become 2 in the future.

(Cherry picked from commit 2b22a663)

Bug: 29054680

Change-Id: I6e3ae3cf18d8c76df94f879c34fb6fde519b89a9
(cherry picked from commit d4421f19)