Add a missing include in DocumentsUI Android.mk.
Add a missing include in DocumentsUI Android.mk.

Without it, perf tests were not built on APCT.

Bug: 27370274
Change-Id: Ie154526d240bb9d1b4cce6fc089d502bf808c366

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base