Remove the 2-level input method system & InputMethodBridge.

ash/root_window_controller.cc

Index: ash/root_window_controller.cc
diff --git a/ash/root_window_controller.cc b/ash/root_window_controller.cc
index 3a5733ed3984ef2d98532e3db4ca8cc84fb20e8b..59728ceb41d3b40bce07e8f075aff4680195a072 100644
--- a/ash/root_window_controller.cc
+++ b/ash/root_window_controller.cc
@@ -235,7 +235,6 @@ class EmptyWindowDelegate : public aura::WindowDelegate {
   gfx::Size GetMaximumSize() const override { return gfx::Size(); }
   void OnBoundsChanged(const gfx::Rect& old_bounds,
                        const gfx::Rect& new_bounds) override {}
-  ui::TextInputClient* GetFocusedTextInputClient() override { return nullptr; }
   gfx::NativeCursor GetCursor(const gfx::Point& point) override {
     return gfx::kNullCursor;
   }