ash: Add launcher overflow bubble.

- Host a LauncherView in bubble to display overflown items;
- Mouse wheel and two-finger scroll to scroll the LauncherView in bubble in case overflow bubble is overflown;
- Fit bubble when items are added/removed;
- Keep launcher bar on screen when the bubble is shown;

BUG=128054
TEST=Verify launcher overflown items are in a bubble instead of menu.


Review URL: https://chromiumcodereview.appspot.com/10659003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@146460 0039d316-1c4b-4281-b951-d872f2087c98
Launcher::~Launcher() {
}

Launcher::~Launcher() {
}
