the official package dev-util/android-tools have been out of date,as there is a very useful command adb sideload which is very convenient to update the android device with official ota, however it is not supported or fully supported with the version 1.0.31 of dev-util/android-tools. but I found that arch have the the x86_64 binary of version 1.0.32 which support it, I think gentoo may have an update of dev-util/android-tools too. Unluckily, I can't get the way of building it myself, finally I just download it from arch repository.
*** This bug has been marked as a duplicate of bug 552198 ***