Add low memory mode option to ART.

Useful so that we match the option I added here:
https://googleplex-android-review.googlesource.com/#/c/328940/

In ART low memory mode reduces the maximum number of histogram
buckets. We also trim no matter the utilization.

Change-Id: I655ba63312c0a6574569cdd5171ca81ea338c2aa
5 files changed