[Settings] Data roaming warning only when turn ON

handlePreferenceTreeClick() goes after setChecked() however
configuration may have been altered within setChecked().

Follow same design within MobileDataPreferenceController to fix this
issue. A boolean state will be maintained as the condition when warning
dialog is required when click.

Bug: 148491064
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=RoamingPreferenceControllerTest
Change-Id: I63c4e2149b0e9efa16fd9ee402652c67eb9c5a4d

tests/robotests/src/com/android/settings/network/telephony/RoamingPreferenceControllerTest.java

@@ -117,10 +117,10 @@ public class RoamingPreferenceControllerTest {
     }
 
     @Test
-    public void handlePreferenceTreeClick_needDialog_showDialog() {
+    public void setChecked_needDialog_showDialog() {
         doReturn(true).when(mController).isDialogNeeded();
 
-        mController.handlePreferenceTreeClick(mPreference);
+        mController.setChecked(true);
 
         verify(mFragmentManager).beginTransaction();
     }