Merge "Use more std::string in fastboot." am: 17f3b1bad7
am: 05ec41963d

* commit '05ec41963d7e219a78ef9ffad6d1b1dcf5f4135c':
  Use more std::string in fastboot.

Change-Id: I819aefd792b1c3cd98403f0b25afa21717086e44