MAGETWO-49766: HTML head Design Configurations are used in Admin

Author: Oleksandr Karpenko

app/code/Magento/Backend/etc/adminhtml/di.xml

@@ -133,4 +133,9 @@
         </arguments>
     </type>
     <preference for="Magento\Framework\App\Router\PathConfigInterface" type="Magento\Backend\Model\AdminPathConfig" />
+    <type name="Magento\Framework\View\Page\Config">
+        <arguments>
+            <argument name="isIncludesAvailable" xsi:type="boolean">false</argument>
+        </arguments>
+    </type>
 </config>

lib/internal/Magento/Framework/View/Page/Config.php

@@ -122,6 +122,11 @@ class Config
      */
     private $areaResolver;
 
+    /**
+     * @var bool
+     */
+    private $isIncludesAvailable;
+
     /**
      * This getter serves as a workaround to add this dependency to this class without breaking constructor structure.
      *
@@ -145,21 +150,24 @@ private function getAreaResolver()
      * @param \Magento\Framework\View\Page\FaviconInterface $favicon
      * @param Title $title
      * @param \Magento\Framework\Locale\ResolverInterface $localeResolver
+     * @param bool $isIncludesAvailable
      */
     public function __construct(
         View\Asset\Repository $assetRepo,
         View\Asset\GroupedCollection $pageAssets,
         App\Config\ScopeConfigInterface $scopeConfig,
         View\Page\FaviconInterface $favicon,
         Title $title,
-        \Magento\Framework\Locale\ResolverInterface $localeResolver
+        \Magento\Framework\Locale\ResolverInterface $localeResolver,
+        $isIncludesAvailable = true
     ) {
         $this->assetRepo = $assetRepo;
         $this->pageAssets = $pageAssets;
         $this->scopeConfig = $scopeConfig;
         $this->favicon = $favicon;
         $this->title = $title;
         $this->localeResolver = $localeResolver;
+        $this->isIncludesAvailable = $isIncludesAvailable;
         $this->setElementAttribute(
             self::ELEMENT_TYPE_HTML,
             self::HTML_ATTRIBUTE_LANG,
@@ -555,7 +563,7 @@ public function getDefaultFavicon()
      */
     public function getIncludes()
     {
-        if (empty($this->includes)) {
+        if (empty($this->includes) && $this->isIncludesAvailable) {
             $this->includes = $this->scopeConfig->getValue(
                 'design/head/includes',
                 \Magento\Store\Model\ScopeInterface::SCOPE_STORE

lib/internal/Magento/Framework/View/Test/Unit/Page/ConfigTest.php

@@ -92,6 +92,9 @@ protected function setUp()
                     'scopeConfig' => $this->scopeConfig,
                     'favicon' => $this->favicon,
                     'localeResolver' => $locale,
+                    'includesAreas' => [
+                        'frontend'
+                    ]
                 ]
             );