Update dirty-image-objects

Numbers 60s after boot on taimen, saves ~4MB of RAM system wide.

Obtained on apps:
system_server
com.android.systemui
com.android.phone
com.android.nfc
com.google.android.networkstack
com.android.bluetooth
com.google.android.apps.nexuslauncher
com.google.android.gms.persistent
com.google.android.as
com.google.process.gservices
com.google.android.gms
com.google.android.inputmethod.latin

Before (measured processes):
                PSS     Private Dirty
    .Boot art     2538     2300        0        0
    .Boot art     2663     2428        0        0
    .Boot art     1962     1676        0        0
    .Boot art      816      540        0        0
    .Boot art     1297     1032        0        0
    .Boot art     1234      968        0        0
    .Boot art     1751     1496        0        0
    .Boot art     2227     1984        0        0
    .Boot art     1114      844        0        0
    .Boot art      772      492        0        0
    .Boot art     2215     1972        0        0
    .Boot art     1213      912        0        0
System wide
     71,282K: .art mmap
         66,418K: .Boot art
          4,864K: .App art

After:
                PSS     Private Dirty
    .Boot art     2447     2216        0        0
    .Boot art     2477     2256        0        0
    .Boot art     1717     1444        0        0
    .Boot art      799      540        0        0
    .Boot art     1268     1020        0        0
    .Boot art     1196      948        0        0
    .Boot art     1703     1464        0        0
    .Boot art     2094     1864        0        0
    .Boot art     1055      804        0        0
    .Boot art      749      484        0        0
    .Boot art     2096     1868        0        0
    .Boot art     1058      772        0        0
System wide
    67,138K: .art mmap
         62,274K: .Boot art
          4,864K: .App art

Bug: 134776403
Test: Reboot and inspect RAM usage
Change-Id: I5c056565a10b0becc4257f051aecc05cef6247dd