Merge changes I7a7510db,Ifb4ae36f,I7ed66ab2,Ia1d00548,I029e91ee, ... into studio-1.4-dev
automerge: 9f42810

* commit '9f4281059d914780f7b83a1d79410b4bd45ab6cd':
  Small build system cleanup to prepare for Qt-based UI.
  emugl: Disable signals from render and window threads.
  android/skin/: Small cleanups to prepare for Qt-based backend.
  android/build: Add support for prebuilt static libraries.
  android/base/System.h: Add addLibrarySearchDir().
  Move '-list-avds' handling to top-level 'emulator' launcher.