Fixed set template syntax in block file

Author: sanganinamrata

app/code/Magento/Theme/Block/Adminhtml/Wysiwyg/Files/Content/Uploader.php

@@ -19,7 +19,7 @@ class Uploader extends \Magento\Backend\Block\Media\Uploader
      *
      * @var string
      */
-    protected $_template = 'browser/content/uploader.phtml';
+    protected $_template = 'Magento_Theme::browser/content/uploader.phtml';
 
     /**
      * @var \Magento\Theme\Helper\Storage

app/code/Magento/Theme/Block/Html/Breadcrumbs.php

@@ -21,7 +21,7 @@ class Breadcrumbs extends \Magento\Framework\View\Element\Template
      *
      * @var string
      */
-    protected $_template = 'html/breadcrumbs.phtml';
+    protected $_template = 'Magento_Theme::html/breadcrumbs.phtml';
 
     /**
      * List of available breadcrumb properties

app/code/Magento/Theme/Block/Html/Header.php

@@ -19,7 +19,7 @@ class Header extends \Magento\Framework\View\Element\Template
      *
      * @var string
      */
-    protected $_template = 'html/header.phtml';
+    protected $_template = 'Magento_Theme::html/header.phtml';
 
     /**
      * Retrieve welcome text

app/code/Magento/Theme/Block/Html/Header/Logo.php

@@ -19,7 +19,7 @@ class Logo extends \Magento\Framework\View\Element\Template
      *
      * @var string
      */
-    protected $_template = 'html/header/logo.phtml';
+    protected $_template = 'Magento_Theme::html/header/logo.phtml';
 
     /**
      * @var \Magento\MediaStorage\Helper\File\Storage\Database