Update to Drupal 8.0.0-beta15. For more information, see: https://www.drupal.org/node/2563023

core/lib/Drupal/Core/Breadcrumb/Breadcrumb.php

@@ -0,0 +1,71 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Breadcrumb\Breadcrumb.
+ */
+
+namespace Drupal\Core\Breadcrumb;
+
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Link;
+
+/**
+ * Used to return generated breadcrumbs with associated cacheability metadata.
+ *
+ * @todo implement RenderableInterface once https://www.drupal.org/node/2529560 lands.
+ */
+class Breadcrumb extends CacheableMetadata {
+
+  /**
+   * An ordered list of links for the breadcrumb.
+   *
+   * @var \Drupal\Core\Link[]
+   */
+  protected $links = [];
+
+  /**
+   * Gets the breadcrumb links.
+   *
+   * @return \Drupal\Core\Link[]
+   */
+  public function getLinks() {
+    return $this->links;
+  }
+
+  /**
+   * Sets the breadcrumb links.
+   *
+   * @param \Drupal\Core\Link[] $links
+   *   The breadcrumb links.
+   *
+   * @return $this
+   *
+   * @throws \LogicException
+   *   Thrown when setting breadcrumb links after they've already been set.
+   */
+  public function setLinks(array $links) {
+    if (!empty($this->links)) {
+      throw new \LogicException('Once breadcrumb links are set, only additional breadcrumb links can be added.');
+    }
+
+    $this->links = $links;
+
+    return $this;
+  }
+
+  /**
+   * Appends a link to the end of the ordered list of breadcrumb links.
+   *
+   * @param \Drupal\Core\Link $link
+   *   The link appended to the breadcrumb.
+   *
+   * @return $this
+   */
+  public function addLink(Link $link) {
+    $this->links[] = $link;
+
+    return $this;
+  }
+
+}

core/lib/Drupal/Core/Breadcrumb/BreadcrumbBuilderInterface.php

@@ -32,9 +32,8 @@ interface BreadcrumbBuilderInterface {
    * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
    *   The current route match.
    *
-   * @return \Drupal\Core\Link[]
-   *   An array of links for the breadcrumb. Returning an empty array will
-   *   suppress all breadcrumbs.
+   * @return \Drupal\Core\Breadcrumb\Breadcrumb
+   *   A breadcrumb.
    */
   public function build(RouteMatchInterface $route_match);
 

core/lib/Drupal/Core/Breadcrumb/BreadcrumbManager.php

@@ -75,7 +75,7 @@ class BreadcrumbManager implements ChainBreadcrumbBuilderInterface {
    * {@inheritdoc}
    */
   public function build(RouteMatchInterface $route_match) {
-    $breadcrumb = array();
+    $breadcrumb = new Breadcrumb();
     $context = array('builder' => NULL);
     // Call the build method of registered breadcrumb builders,
     // until one of them returns an array.
@@ -85,11 +85,9 @@ class BreadcrumbManager implements ChainBreadcrumbBuilderInterface {
         continue;
       }
 
-      $build = $builder->build($route_match);
+      $breadcrumb = $builder->build($route_match);
 
-      if (is_array($build)) {
-        // The builder returned an array of breadcrumb links.
-        $breadcrumb = $build;
+      if ($breadcrumb instanceof Breadcrumb) {
         $context['builder'] = $builder;
         break;
       }
@@ -99,7 +97,7 @@ class BreadcrumbManager implements ChainBreadcrumbBuilderInterface {
     }
     // Allow modules to alter the breadcrumb.
     $this->moduleHandler->alter('system_breadcrumb', $breadcrumb, $route_match, $context);
-    // Fall back to an empty breadcrumb.
+
     return $breadcrumb;
   }