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/location/ScanningSettings.java

@@ -33,7 +33,7 @@ public class ScanningSettings extends SettingsPreferenceFragment {
     private static final String KEY_BLUETOOTH_SCAN_ALWAYS_AVAILABLE = "bluetooth_always_scanning";
 
     @Override
-    protected int getMetricsCategory() {
+    public int getMetricsCategory() {
         return MetricsEvent.LOCATION_SCANNING;
     }