chromeos: fix focus for mushrome

ash/aura/shell_port_classic.cc

Index: ash/aura/shell_port_classic.cc
diff --git a/ash/aura/shell_port_classic.cc b/ash/aura/shell_port_classic.cc
index e5e9760f8af7131430dda345d2c64f01ce62935e..766ae123ad3c22b46a55d32b78b402ff8085e5f4 100644
--- a/ash/aura/shell_port_classic.cc
+++ b/ash/aura/shell_port_classic.cc
@@ -249,6 +249,9 @@ std::unique_ptr<AshWindowTreeHost> ShellPortClassic::CreateAshWindowTreeHost(
   return nullptr;
 }
 
+void ShellPortClassic::OnCreatedRootWindowContainers(
+    RootWindowController* root_window_controller) {}
+
 void ShellPortClassic::CreatePrimaryHost() {
   Shell::Get()->window_tree_host_manager()->Start();
   AshWindowTreeHostInitParams ash_init_params;