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 9d15218621caed7de0e2b2a5fbb747e93603d93b..1853dc82446c404d2bb1c9ea6498a364f716fe84 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -339,6 +339,10 @@ void Shell::ToggleAppList(aura::Window* window) {
       GetDisplayIdForWindow(window));
 }
 
+bool Shell::IsApplistVisible() const {
+  return delegate_->GetAppListPresenter()->IsVisible();
+}
+
 bool Shell::GetAppListTargetVisibility() const {
   return delegate_->GetAppListPresenter()->GetTargetVisibility();
 }