Implement virtual keyboard hiding.

ui/keyboard/keyboard_ui_handler.h

Index: ui/keyboard/keyboard_ui_handler.h
diff --git a/ui/keyboard/keyboard_ui_handler.h b/ui/keyboard/keyboard_ui_handler.h
index 719852fdb97d223c65c19bee18c1b421021b07aa..3c14f7473e5c75419ee3c86bc756575f3780acd6 100644
--- a/ui/keyboard/keyboard_ui_handler.h
+++ b/ui/keyboard/keyboard_ui_handler.h
@@ -34,6 +34,9 @@ class KeyboardUIHandler : public content::WebUIMessageHandler {
   // released, a virtual key code, and the state of the shift key.
   void HandleSendKeyEventMessage(const base::ListValue* args);
 
+  // Callback for the "hideKeyboard" message.
+  void HandleHideKeyboard(const base::ListValue* args);
+
   DISALLOW_COPY_AND_ASSIGN(KeyboardUIHandler);
 };