Add a mutability flag to the PendingIntent

- Request from Android Platform Security team.
  go/immutable-pendingintents

Bug: 170162129
Test:
1. adb shell am start -a
android.settings.panel.action.INTERNET_CONNECTIVITY
2. make RunSettingsRoboTests ROBOTEST_FILTER=WifiSliceTest
Change-Id: If3032959649206f2fb6736244d7aa8b9a8419378

src/com/android/settings/wifi/slice/WifiSlice.java

@@ -224,7 +224,7 @@ public class WifiSlice implements CustomSliceable {
     private SliceAction getActivityAction(int requestCode, Intent intent, IconCompat icon,
             CharSequence title) {
         final PendingIntent pi = PendingIntent.getActivity(mContext, requestCode, intent,
-                0 /* flags */);
+                PendingIntent.FLAG_IMMUTABLE /* flags */);
         return SliceAction.createDeeplink(pi, icon, ListBuilder.ICON_IMAGE, title);
     }
 
@@ -289,7 +289,7 @@ public class WifiSlice implements CustomSliceable {
     private PendingIntent getPrimaryAction() {
         final Intent intent = getIntent();
         return PendingIntent.getActivity(mContext, 0 /* requestCode */,
-                intent, 0 /* flags */);
+                intent, PendingIntent.FLAG_IMMUTABLE /* flags */);
     }
 
     private Set<String> getKeywords() {