Document ContentProvider's API a bit more explicitly
Document ContentProvider's API a bit more explicitly

In particular, call out parameters that must not be null.

Change-Id: I67af73163e36efefefa7df86499937f998be5b00

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