Log visibility change for all fragments.

Bug: 30681771
Test: SettingsUnitTests

Refactor visibility logging from InstrumentedFragment into a mixin. And
apply mixin in remaining fragments.

Change-Id: Ibbb59904336254a3e4bb9e8c7d0b36e5a6bc2622

src/com/android/settings/inputmethod/KeyboardLayoutPickerFragment2.java

@@ -71,7 +71,7 @@ public final class KeyboardLayoutPickerFragment2 extends SettingsPreferenceFragm
     public static final String EXTRA_INPUT_METHOD_SUBTYPE = "input_method_subtype";
 
     @Override
-    protected int getMetricsCategory() {
+    public int getMetricsCategory() {
         return MetricsEvent.INPUTMETHOD_KEYBOARD;
     }