Allow LOCAL_ASSET_DIR point to nonexistent dir
Allow LOCAL_ASSET_DIR point to nonexistent dir

LOCAL_ASSET_DIR may point to a dir generated during the build process.
We have done similiar things to LOCAL_RESOURCE_DIR.

(cherry picked from commit bfcdf060bab129581acff32eb70896f719162bc9)

Bug: 16563899
Change-Id: Iaa72196e1e6350ae0720f8a4e0abc68d8d7ed642

xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build