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 57993d5a7a9a7d0197da1222718ca8f9eaa41ea6..da152e749fe3a187cc9898d6e37d822c5038b33a 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -333,6 +333,10 @@ void Shell::ToggleAppList(aura::Window* window) {
       GetDisplayIdForWindow(window));
 }
 
+bool Shell::IsApplistVisible() const {
+  return delegate_->GetAppListPresenter()->IsVisible();
+}
+
 bool Shell::GetAppListTargetVisibility() const {
   return delegate_->GetAppListPresenter()->GetTargetVisibility();
 }