Use arrays for dense_ in SparseArray<> and SparseSet.

Thus providing constant-time allocation once again...

Change-Id: I25dc799c1c57e65c0cfdccc0e65f7e963eba5c1b
Reviewed-on: https://code-review.googlesource.com/17510
Reviewed-by: Paul Wankadia <junyer@google.com>
2 files changed