updated code following code review & backward compatible development guide

# Conflicts:
#	app/code/Magento/Customer/Test/Unit/Model/Checkout/ConfigProviderTest.php

Author: Tommy Quissens

app/code/Magento/Customer/Model/Checkout/ConfigProvider.php

@@ -22,6 +22,12 @@ class ConfigProvider implements ConfigProviderInterface
 
     /**
      * @var UrlInterface
+     * @deprecated
+     */
+    protected $urlBuilder;
+
+    /**
+     * @var Url
      */
     protected $customerUrl;
 
@@ -31,18 +37,21 @@ class ConfigProvider implements ConfigProviderInterface
     protected $scopeConfig;
 
     /**
-     * @param Url $customerUrl
+     * @param UrlInterface $urlBuilder
      * @param StoreManagerInterface $storeManager
      * @param ScopeConfigInterface $scopeConfig
+     * @param Url $customerUrl
      */
     public function __construct(
-        Url $customerUrl,
+        UrlInterface $urlBuilder,
         StoreManagerInterface $storeManager,
-        ScopeConfigInterface $scopeConfig
+        ScopeConfigInterface $scopeConfig,
+        Url $customerUrl = null
     ) {
-        $this->customerUrl = $customerUrl;
+        $this->urlBuilder=$urlBuilder;
         $this->storeManager = $storeManager;
         $this->scopeConfig = $scopeConfig;
+        $this->customerUrl = $customerUrl ?? \Magento\Framework\App\ObjectManager::getInstance()->get(\Magento\Customer\Model\Url::class);
     }
 
     /**

app/code/Magento/Customer/Test/Unit/Model/Checkout/ConfigProviderTest.php

@@ -1,6 +1,6 @@
 <?php
 /**
- * Copyright © 2013-2017 Magento, Inc. All rights reserved.
+ * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
 namespace Magento\Customer\Test\Unit\Model\Checkout;
@@ -14,7 +14,7 @@
 use Magento\Customer\Model\Form;
 use Magento\Store\Model\ScopeInterface;
 
-class ConfigProviderTest extends \PHPUnit_Framework_TestCase
+class ConfigProviderTest extends \PHPUnit\Framework\TestCase
 {
     /**
      * @var ConfigProvider
@@ -29,7 +29,7 @@ class ConfigProviderTest extends \PHPUnit_Framework_TestCase
     /**
      * @var UrlInterface|\PHPUnit_Framework_MockObject_MockObject
      */
-    protected $customerUrl;
+    protected $urlBuilder;
 
     /**
      * @var ScopeConfigInterface|\PHPUnit_Framework_MockObject_MockObject
@@ -41,6 +41,11 @@ class ConfigProviderTest extends \PHPUnit_Framework_TestCase
      */
     protected $store;
 
+    /**
+     * @var Url|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $customerUrl;
+
     protected function setUp()
     {
         $this->storeManager = $this->getMockForAbstractClass(
@@ -50,10 +55,12 @@ protected function setUp()
             false
         );
 
-        $this->customerUrl = $this->getMockBuilder(\Magento\Customer\Model\Url::class)
-        ->disableOriginalConstructor()
-        ->setMethods(['getLoginUrl'])
-        ->getMock();
+        $this->urlBuilder = $this->getMockForAbstractClass(
+            \Magento\Framework\UrlInterface::class,
+            [],
+            '',
+            false
+        );
 
         $this->scopeConfig = $this->getMockForAbstractClass(
             \Magento\Framework\App\Config\ScopeConfigInterface::class,
@@ -71,10 +78,16 @@ protected function setUp()
             ['getBaseUrl']
         );
 
+        $this->customerUrl = $this->getMockBuilder(\Magento\Customer\Model\Url::class)
+            ->disableOriginalConstructor()
+            ->setMethods(['getLoginUrl'])
+            ->getMock();
+
         $this->provider = new ConfigProvider(
-            $this->customerUrl,
+            $this->urlBuilder,
             $this->storeManager,
-            $this->scopeConfig
+            $this->scopeConfig,
+            $this->customerUrl
         );
     }