Make keyboard controller a singleton.

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 1de832c0c57f5b327996cc56556cd9d5bdbc89ab..e91c5b828e740b115abfbba57b5f48607d0b3b31 100644
--- a/ui/keyboard/keyboard_controller.cc
+++ b/ui/keyboard/keyboard_controller.cc
@@ -178,6 +178,9 @@ void CallbackAnimationObserver::OnLayerAnimationAborted(
   animator_->RemoveObserver(this);
 }
 
+// static
+KeyboardController* KeyboardController::instance_ = NULL;
+
 KeyboardController::KeyboardController(KeyboardControllerProxy* proxy)
     : proxy_(proxy),
       input_method_(NULL),
@@ -197,6 +200,18 @@ KeyboardController::~KeyboardController() {
     input_method_->RemoveObserver(this);
 }
 
+// static
+void KeyboardController::ResetInstance(KeyboardController* controller) {
+  if (instance_ && instance_ != controller)
+    delete instance_;
+  instance_ = controller;
+}
+
+// static
+KeyboardController* KeyboardController::GetInstance() {
+  return instance_;
+}
+
 aura::Window* KeyboardController::GetContainerWindow() {
   if (!container_.get()) {
     container_.reset(new aura::Window(