Fix missing incremental process starting position of LRU list

When searching insertion position for a process with clients activities,
if the position goes to mLruProcessActivityStart but we don't increase
mLruProcessActivityStart, it will be like hide a slot. Then when removing
the process from LRU, the starting position will be decreased, that causes
a slot is lost. After this condition happens many times, the starting
position (mLruProcessServiceStart in the practical case) becomes a negative
number which leads to IndexOutOfBoundsException.

The expected example:
 Assume to insert a new process X to [2]:
  [0]A
  [1]B
  [2]C <- mLruProcess(Activity/Service)Start
  [3]D
 After insertion, the starting position increased:
  [0]A
  [1]B
  [2]X
  [3]C <- mLruProcess(Activity/Service)Start
  [4]D

Bug: 126427214
Test: Build system/extras/tests/memeater and push to device.
      Execute multiple memeater instances to consume most of RAM.
      Observe home is being killed and restarted frequently for a
      long time without IndexOutOfBoundsException from LRU list.

Change-Id: I8a925aa320141e55e18fa4312ba91cb628bcc47d