Add an activity that starts DataUsageList fragment for mobile.

We are providing an itent and a corresponding activity to show
"Mobile data usage" fragment, so that "Mobile network setting"
who lives in phone apk can use that intent to open it.

Bug: 62201918
Test: Manual
Change-Id: I862f8bc90f9456f91b436d26472cce23c837a777

src/com/android/settings/Settings.java

@@ -90,6 +90,7 @@ public class Settings extends SettingsActivity {
     public static class CryptKeeperSettingsActivity extends SettingsActivity { /* empty */ }
     public static class DeviceAdminSettingsActivity extends SettingsActivity { /* empty */ }
     public static class DataUsageSummaryActivity extends SettingsActivity { /* empty */ }
+    public static class MobileDataUsageListActivity extends SettingsActivity { /* empty */ }
     public static class ConfigureWifiSettingsActivity extends SettingsActivity { /* empty */ }
     public static class SavedAccessPointsSettingsActivity extends SettingsActivity { /* empty */ }
     public static class TextToSpeechSettingsActivity extends SettingsActivity { /* empty */ }

src/com/android/settings/core/gateway/SettingsGateway.java

@@ -62,6 +62,7 @@ import com.android.settings.bluetooth.BluetoothDeviceDetailsFragment;
 import com.android.settings.bluetooth.BluetoothSettings;
 import com.android.settings.connecteddevice.ConnectedDeviceDashboardFragment;
 import com.android.settings.dashboard.SupportFragment;
+import com.android.settings.datausage.DataUsageList;
 import com.android.settings.datausage.DataUsageSummary;
 import com.android.settings.deletionhelper.AutomaticStorageManagerSettings;
 import com.android.settings.development.DevelopmentSettings;
@@ -251,6 +252,7 @@ public class SettingsGateway {
             WebViewAppPicker.class.getName(),
             LockscreenDashboardFragment.class.getName(),
             BluetoothDeviceDetailsFragment.class.getName(),
+            DataUsageList.class.getName()
     };
 
     public static final String[] SETTINGS_FOR_RESTRICTED = {