MAGETWO-52478: CreateOnlineCreditMemoBraintreePaypalTest is failing on closing popup window

- Added fix for tests from shopping cart

Author: rliukshyn

dev/tests/functional/tests/app/Magento/Braintree/Test/TestStep/CheckoutWithPaypalFromCartStep.php

@@ -37,8 +37,8 @@ public function __construct(CheckoutCart $checkoutCart)
     public function run()
     {
         $this->checkoutCart->open();
-        $this->checkoutCart->getCartBlock()
+        $currentWindow = $this->checkoutCart->getCartBlock()
             ->braintreePaypalCheckout();
-        $this->checkoutCart->getBraintreePaypalBlock()->process();
+        $this->checkoutCart->getBraintreePaypalBlock()->process($currentWindow);
     }
 }

dev/tests/functional/tests/app/Magento/Braintree/Test/TestStep/CheckoutWithPaypalFromMinicartStep.php

@@ -61,7 +61,7 @@ public function run()
     {
         $product = reset($this->products);
         $this->browser->open($_ENV['app_frontend_url'] . $product->getUrlKey() . '.html');
-        $this->catalogProductView->getViewBlock()->braintreePaypalCheckout();
-        $this->catalogProductView->getBraintreePaypalBlock()->process();
+        $parentWindow = $this->catalogProductView->getViewBlock()->braintreePaypalCheckout();
+        $this->catalogProductView->getBraintreePaypalBlock()->process($parentWindow);
     }
 }

dev/tests/functional/tests/app/Magento/Catalog/Test/Block/Product/View.php

@@ -302,11 +302,12 @@ public function inContextPaypalCheckout()
 
     /**
      * Press 'Check out with Braintree PayPal' button.
-     *
-     * @return void
+     * 
+     * @return string
      */
     public function braintreePaypalCheckout()
     {
+        $currentWindow = $this->browser->getCurrentWindow();
         /** @var \Magento\Checkout\Test\Block\Cart\Sidebar $miniCart */
         $miniCart = $this->blockFactory->create(
             '\Magento\Checkout\Test\Block\Cart\Sidebar',
@@ -315,6 +316,7 @@ public function braintreePaypalCheckout()
 
         $miniCart->openMiniCart();
         $miniCart->clickBraintreePaypalButton();
+        return $currentWindow;
     }
 
     /**

dev/tests/functional/tests/app/Magento/Checkout/Test/Block/Cart.php

@@ -152,12 +152,14 @@ public function getOnepageLinkBlock()
     /**
      * Click "Check out with Braintree PayPal" button.
      *
-     * @return void
+     * @return string
      */
     public function braintreePaypalCheckout()
     {
+        $currentWindow = $this->browser->getCurrentWindow();
         $this->_rootElement->find($this->braintreePaypalCheckoutButton, Locator::SELECTOR_XPATH)
             ->click();
+        return $currentWindow;
     }
 
     /**