Add MD ink drop ripple to app list button

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 5036193ddddfa135a165aff7dc5020427e5444f8..c331e21aadeb721fa853dfcab43b1360a25c9524 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -335,6 +335,10 @@ void Shell::ToggleAppList(aura::Window* window) {
       GetDisplayIdForWindow(window));
 }
 
+bool Shell::IsApplistVisible() const {
+  return delegate_->GetAppListPresenter()->IsVisible();
+}
+
 bool Shell::GetAppListTargetVisibility() const {
   return delegate_->GetAppListPresenter()->GetTargetVisibility();
 }