Tune rosalloc buffer sizes.

We now use one-page buffers for size brackets 4-7, instead of two-page
buffers, and the first 8 size brackets for thread-local allocations,
instead of 11.

No slowdown observed with MemAllocTest, EvaluateAndApplyChanges, and
BinaryTrees.

(cherrypick commit c4cd95fa37b7138a0fa26d07c235aa409542aecd)

Bug: 18377775
Change-Id: I311f3adf9cab660d258833b17df7e6d905f73c72
2 files changed