compare android::Vector and std::vector

Have been wondering for a while.

Test: libutils_benchmark
--------------------------------------------------------------------
Benchmark                          Time             CPU   Iterations
--------------------------------------------------------------------
BM_fill_android_vector          24.6 ns         24.5 ns     28207074
BM_fill_std_vector              5.24 ns         5.21 ns    130675479
BM_prepend_android_vector       5783 ns         5770 ns       100000
BM_prepend_std_vector           5731 ns         5717 ns       100000

Change-Id: Ie296ce2c4395121b6a456d57421f820909418afe