Change some functions in ImeEngineObserver as not ChromeOS-only.

chrome/browser/extensions/api/input_ime/input_ime_api_nonchromeos.cc

Index: chrome/browser/extensions/api/input_ime/input_ime_api_nonchromeos.cc
diff --git a/chrome/browser/extensions/api/input_ime/input_ime_api_nonchromeos.cc b/chrome/browser/extensions/api/input_ime/input_ime_api_nonchromeos.cc
index 34dc1457781e56c35e666e8e9a48637ff74e5fdd..5f99f80c9f1018c03b8d387b722f5dc3ef74a751 100644
--- a/chrome/browser/extensions/api/input_ime/input_ime_api_nonchromeos.cc
+++ b/chrome/browser/extensions/api/input_ime/input_ime_api_nonchromeos.cc
@@ -47,6 +47,10 @@ class ImeObserverNonChromeOS : public ui::ImeObserver {
         ->DispatchEventToExtension(extension_id_, std::move(event));
   }
 
+  std::string GetCurrentScreenType() override {
+    return "normal";
+  }
+
   DISALLOW_COPY_AND_ASSIGN(ImeObserverNonChromeOS);
 };