Android: whitelist MADV_RANDOM and MADV_NORMAL.

Extend seccomp_bpf to allow MADV_RANDOM and MADV_NORMAL for the madvise()
syscall. These are used to control code page memory footprint, particularly on
android.

Bug: 758566
Cq-Include-Trybots: master.tryserver.chromium.android:android_compile_x64_dbg;master.tryserver.chromium.android:android_compile_x86_dbg
Change-Id: I9d87af4453d19a1391053ffc56f1eab85a2ad231
Reviewed-on: https://chromium-review.googlesource.com/1150176
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Reviewed-by: Chris Palmer <palmer@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584845}

sandbox/linux/seccomp-bpf-helpers/baseline_policy.cc

@@ -174,9 +174,11 @@ ResultExpr EvaluateSyscallImpl(int fs_denied_errno,
   }
 
   if (sysno == __NR_madvise) {
-    // Only allow MADV_DONTNEED and MADV_FREE.
+    // Only allow MADV_DONTNEED, MADV_RANDOM, MADV_NORMAL and MADV_FREE.
     const Arg<int> advice(2);
-    return If(AnyOf(advice == MADV_DONTNEED
+    return If(AnyOf(advice == MADV_DONTNEED,
+                    advice == MADV_RANDOM,
+                    advice == MADV_NORMAL
 #if defined(MADV_FREE)
                     // MADV_FREE was introduced in Linux 4.5 and started being
                     // defined in glibc 2.24.