droiddoc change: add flag to offline docs build to signal
that we're building offline docs so that we do not generate
all of the web pages for the sample apps source code.

This depends on change 33762 (sha I06c40454), meaning, this
will break the build without that.

Change-Id: Id2ee762de13f23c3da15d55e763c1838b11ac31c
1 file changed