Use new VolumeInfo helper methods.

Makes it clearer if we're checking for readable/writable state,
and puts emulated/private conversion logic in single place.

Bug: 19993667
Change-Id: I953f5c184ca62afc631d855e64cd8a4972320148

src/com/android/settings/deviceinfo/StorageSettings.java

@@ -186,7 +186,7 @@ public class StorageSettings extends SettingsPreferenceFragment implements Index
             return true;
 
         } else if (vol.getType() == VolumeInfo.TYPE_PUBLIC) {
-            if (vol.getState() == VolumeInfo.STATE_MOUNTED) {
+            if (vol.isMountedReadable()) {
                 startActivity(vol.buildBrowseIntent());
                 return true;
             } else {