Extract counting of installed apps into helper class

This CL extracts the code that counts the number of installed apps
for a set of users from ManageApplications to a helper class,
InstalledAppCounter. The new helper is designed to be unit-testable
(PackageManager dependencies are injected via a new PackageManagerWrapper
abstraction) and customizable (the set of users for which to count is
specified by subclasses).

The CL adds a unit test for the InstalledAppCounter as well.

Test: make RunSettingsRoboTests
Bug: 32692748
Change-Id: Ie7fbd40d9dd998b27f1f9de227b6a187b5c9d315

src/com/android/settings/applications/NotificationApps.java

@@ -17,10 +17,17 @@ package com.android.settings.applications;
 import android.app.Activity;
 import android.content.Context;
 import android.content.pm.ApplicationInfo;
+import android.content.pm.PackageManager;
+import android.content.pm.UserInfo;
+import android.os.UserHandle;
+import android.os.UserManager;
+
 import com.android.settings.R;
 import com.android.settings.dashboard.SummaryLoader;
 import com.android.settings.notification.NotificationBackend;
 
+import java.util.List;
+
 /**
  * Extension of ManageApplications with no changes other than having its own
  * SummaryProvider.
@@ -42,12 +49,18 @@ public class NotificationApps extends ManageApplications {
         @Override
         public void setListening(boolean listening) {
             if (listening) {
-                new AppCounter(mContext) {
+                new AppCounter(mContext,
+                        new PackageManagerWrapperImpl(mContext.getPackageManager())) {
                     @Override
                     protected void onCountComplete(int num) {
                         updateSummary(num);
                     }
 
+                    @Override
+                    protected List<UserInfo> getUsersToCount() {
+                         return mUm.getProfiles(UserHandle.myUserId());
+                    }
+
                     @Override
                     protected boolean includeInCount(ApplicationInfo info) {
                         return mNotificationBackend.getNotificationsBanned(info.packageName,