lmkd: Do not treat RSS=0 as a sign of a process being dead

With kernel SPLIT_RSS_COUNTING feature it is possible for a valid
process to report RSS of 0 size when reading /proc/pid/statm. This
happens because split RSS accounting aggregates per-thread counters
asynchronously and depending on the timing of the read, reported
value can be inaccurate and occasionally be 0.
lmkd currently treats processes reporting RSS of 0 as dead and
removes them from the list of processes being tracked. This might
lead to a valid process becoming unkillable.
Change lmkd to stop treating RSS of 0 as a sign of a dead process.

Bug: 160199622
Test: set ro.lmk.kill_heaviest_task=true and hack kernel to report RSS=0
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: Ia311d2f98649c92d1a487657f94ea51f57813b73

lmkd.cpp

@@ -1898,7 +1898,7 @@ static struct proc *proc_get_heaviest(int oomadj) {
     while (curr != head) {
         int pid = ((struct proc *)curr)->pid;
         int tasksize = proc_get_size(pid);
-        if (tasksize <= 0) {
+        if (tasksize < 0) {
             struct adjslot_list *next = curr->next;
             pid_remove(pid);
             curr = next;