Skip writing zeroes to java allocated memory.

If pixel memory was just allocated by Java, tell our decoders not
to write 0s, since the memory was initialized to 0. Likewise,
when drawing to a bitmap with memory just allocated by Java, do
not erase to 0.

Depends on a change to external/skia to add the new option on
image decoders:
https://googleplex-android-review.git.corp.google.com/362663

BUG:10016979
Change-Id: I9a3dc969870f8516e7d8495fe96d0a6b8225eda2