Fix: null name is added when using android_set_process_profiles

This CL fixes a bug that null names are passed when profiles are set
via android_set_process_profiles. This is because the `profiles_` vector
was initialized with the number of task profiles and then we append the
actual task profile names to the vector. As a result, when {"a", "b"}
was given, the vector ended up having {"", "", "a", "b"}. Fixing this by
correctly using reserve().

Bug: N/A
Test: m
Change-Id: I28d6c2e891b01a2d3a8a88d9d0652fe0dbffac96