Optimize code that only uses PageMap call.

Some code only wants to use PageMap to determine whether pages are
mapped in to memory. Modify the code to optimize this path.

- Add a function that doesn't read all of usage stats data for every
  map. This operation is extremely expensive, and some code doesn't
  care about it.
- Optimize the PageMap call to do a single read instead of a single
  read per page.
- Add unit tests for these changes.

Bug: 136245508

Test: Ran new unit tests.
Test: Ran procrank and verified data looks good.
Test: Ran DexDiag art tests.
Change-Id: I37d03f2584551d26cb20be3abacdb958111d4eca
3 files changed