Add subtext for default keyboard layout.

Bug: 27742933
Change-Id: I51bec339c0cbcfb114f85758b6a227deb57a69e2

res/values/strings.xml

@@ -3667,6 +3667,9 @@
         e.g. English (US) - X Keyboard -->
     <string name="physical_device_title"><xliff:g id="input_method_subtype" example="English (US)">%1$s</xliff:g> - <xliff:g id="input_method_editor" example="X Keyboard">%2$s</xliff:g></string>
 
+    <!-- Summary text for keyboards when no layout has been selected. [CHAR LIMIT=35] -->
+    <string name="default_keyboard_layout">Default</string>
+
     <!-- On Languages & input settings screen, heading. Inside the "Languages & input settings" screen, this is the header for settings that relate to mouse and trackpad devices. [CHAR LIMIT=40] -->
     <string name="pointer_settings_category">Mouse/trackpad</string>
     <!-- On Languages & input settings screen, setting summary.  Setting for mouse pointer speed. [CHAR LIMIT=35] -->

src/com/android/settings/inputmethod/PhysicalKeyboardFragment.java

@@ -152,6 +152,9 @@ public final class PhysicalKeyboardFragment extends SettingsPreferenceFragment
                     KeyboardLayout layout = info.mLayout;
                     if (layout != null) {
                         pref.setSummary(layout.getLabel());
+                    } else {
+                        pref.setSummary(
+                                getPrefContext().getString(R.string.default_keyboard_layout));
                     }
                     pref.setOnPreferenceClickListener(preference -> {
                         showKeyboardLayoutScreen(