Created new public API so applications can customize its metered network
usage while running in background.

The new API is 'int getRestrictBackgroundStatus()' and returns the
following values:

 - RESTRICT_BACKGROUND_STATUS_DISABLED: no restrictions
 - RESTRICT_BACKGROUND_STATUS_WHITELISTED: restriction but app is
   whitelisted
 - RESTRICT_BACKGROUND_STATUS_ENABLED: full restriction

The proper way to interprete these values for using metered networks
while running on background is:

 - When disabled, there is no restriction and the application could use the
   metered networks freely.

 - When whitelisted, the application can use the metered network, but should try
   to minimize the usage.

 - When enabled, the application should not try to use metered networks at
   all, since the usage will be denied.

BUG: 26451391
Change-Id: If07d42bb88e4c02802df0234861f38aef2cfead7
diff --git a/services/core/java/com/android/server/net/NetworkPolicyManagerService.java b/services/core/java/com/android/server/net/NetworkPolicyManagerService.java
index 38ebc80..2658489 100644
--- a/services/core/java/com/android/server/net/NetworkPolicyManagerService.java
+++ b/services/core/java/com/android/server/net/NetworkPolicyManagerService.java
@@ -31,6 +31,9 @@
 import static android.net.ConnectivityManager.CONNECTIVITY_ACTION;
 import static android.net.ConnectivityManager.TYPE_MOBILE;
 import static android.net.ConnectivityManager.TYPE_WIMAX;
+import static android.net.ConnectivityManager.RESTRICT_BACKGROUND_STATUS_DISABLED;
+import static android.net.ConnectivityManager.RESTRICT_BACKGROUND_STATUS_ENABLED;
+import static android.net.ConnectivityManager.RESTRICT_BACKGROUND_STATUS_WHITELISTED;
 import static android.net.ConnectivityManager.isNetworkTypeMobile;
 import static android.net.NetworkPolicy.CYCLE_NONE;
 import static android.net.NetworkPolicy.LIMIT_DISABLED;
@@ -1873,6 +1876,20 @@
     }
 
     @Override
+    public int getRestrictBackgroundByCaller() {
+        mContext.enforceCallingOrSelfPermission(ACCESS_NETWORK_STATE, TAG);
+        final int uid = Binder.getCallingUid();
+        synchronized (mRulesLock) {
+            if (!mRestrictBackground) {
+                return RESTRICT_BACKGROUND_STATUS_DISABLED;
+            }
+            return mRestrictBackgroundWhitelistUids.get(uid)
+                    ? RESTRICT_BACKGROUND_STATUS_WHITELISTED
+                    : RESTRICT_BACKGROUND_STATUS_ENABLED;
+        }
+    }
+
+    @Override
     public boolean getRestrictBackground() {
         mContext.enforceCallingOrSelfPermission(MANAGE_NETWORK_POLICY, TAG);