Gallery2: fix two same albums come out after double click tags

When user click group by tags in albumpage,it will start
albumsetpage to make gallery display the pictures which
are sorted by tags.Then albumpsetpage will new a thread
to load albums data.So two threads will be created if user
click group by tags twice quickly.So the data will be handled
by two thread.So the size of the albums will be add twice.
So two same albums came out.

For thread security,we add a synchronized to make sure the mAlbums can
be only handled by one thread.

CRs-Fixed: 562742

Change-Id: Ib1e2356fe25811c6d5d083cedd1861ce3bf7dea3
Gallery2: The menu bar will not flicker.

When select/unselect items,the operation of menu bar is set
visible or invisible repeatly which cause the menu bar flicker.

Add a condition to judge whether the menu bar should invisible at the
beginning. And make the Share operation invisible only when the num of
selection picture is over 300.

CRs-Fixed: 567580

Change-Id: I58c724f7426a33f8b94bac174fc4d512a7aa6c49