Log source with visibility change

- Add a method in VisibilityLoggerMixin to log visible event using
  LogMaker, which allows logging additional FIELD_CONTEXT field.
- In Utils.startFragment, add current page's metricsCategory as an extra
  to next page.
- In next page's onResume(), extract the previous page's metricsCategory
  and send it to VisibilityLoggerMixin.visible()
- Update all caller with additional paramters

Change-Id: I8e1f2597fa465b7d3aa16fa1d21c052a3219694a
Fix: 35359289
Test: RunSettingsRoboTests

src/com/android/settings/vpn2/VpnSettings.java

@@ -405,8 +405,8 @@ public class VpnSettings extends RestrictedSettingsFragment implements
                 ConfigDialogFragment.show(VpnSettings.this, pref.getProfile(), true /* editing */,
                         true /* exists */);
             } else if (p instanceof AppPreference) {
-                AppPreference pref = (AppPreference) p;;
-                AppManagementFragment.show(getPrefContext(), pref);
+                AppPreference pref = (AppPreference) p;
+                AppManagementFragment.show(getPrefContext(), pref, getMetricsCategory());
             }
         }
     };