Respect android:allowClearUserData=false during restore

Ordinarily we wipe the data of apps we are restoring.  This is problematic for
packages that expect that their data can never be wiped back to nothing,
especially system packages, so we now respect the android:allowClearUserData
manifest attribute.

services/java/com/android/server/BackupManagerService.java

@@ -529,6 +529,19 @@ class BackupManagerService extends IBackupManager.Stub {
 
     // clear an application's data, blocking until the operation completes or times out
     void clearApplicationDataSynchronous(String packageName) {
+        // Don't wipe packages marked allowClearUserData=false
+        try {
+            PackageInfo info = mPackageManager.getPackageInfo(packageName, 0);
+            if ((info.applicationInfo.flags & ApplicationInfo.FLAG_ALLOW_CLEAR_USER_DATA) == 0) {
+                if (DEBUG) Log.i(TAG, "allowClearUserData=false so not wiping "
+                        + packageName);
+                return;
+            }
+        } catch (NameNotFoundException e) {
+            Log.w(TAG, "Tried to clear data for " + packageName + " but not found");
+            return;
+        }
+
         ClearDataObserver observer = new ClearDataObserver();
 
         synchronized(mClearDataLock) {