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 2ee91955bc85a269fe06a47125588f66479d5003..2a7f8dd342842f353356a3aeea142feaa0212f0f 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -340,6 +340,10 @@ void Shell::ToggleAppList(aura::Window* window) {
       GetDisplayIdForWindow(window));
 }
 
+bool Shell::IsApplistVisible() const {
+  return delegate_->GetAppListPresenter()->IsVisible();
+}
+
 bool Shell::GetAppListTargetVisibility() const {
   return delegate_->GetAppListPresenter()->GetTargetVisibility();
 }