text input focus: Supports Window::GetFocusedTextInputClient.

ui/keyboard/keyboard_controller.cc

Index: ui/keyboard/keyboard_controller.cc
diff --git a/ui/keyboard/keyboard_controller.cc b/ui/keyboard/keyboard_controller.cc
index 34d5a68310f526f2313b1caaed8758b1c716ad7f..0ae21bc2120fe8a07a04f5cdcc047f49afb3c3ec 100644
--- a/ui/keyboard/keyboard_controller.cc
+++ b/ui/keyboard/keyboard_controller.cc
@@ -93,6 +93,9 @@ class KeyboardWindowDelegate : public aura::WindowDelegate {
                        const gfx::Rect& new_bounds) override {
     bounds_ = new_bounds;
   }
+  ui::TextInputClient* GetFocusedTextInputClient() override {
+    return nullptr;
+  }
   gfx::NativeCursor GetCursor(const gfx::Point& point) override {
     return gfx::kNullCursor;
   }