Fix a variable name reference in Activity docs.
Fix a variable name reference in Activity docs.

Change-Id: Ib0fd1c6b75f73a4470d2cb790884490a3efa8716

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