Block Editor: Add an `is_block_editor()` method to `WP_Screen`.

This method allows checking (or setting) whether the block editor is loading on the current screen.

See #45037.


Built from https://develop.svn.wordpress.org/branches/5.0@43777


git-svn-id: http://core.svn.wordpress.org/branches/5.0@43606 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/class-wp-screen.php

@@ -181,6 +181,14 @@ final class WP_Screen {
 	 */
 	private $_screen_settings;
 
+	/**
+	 * Whether the screen is using the block editor.
+	 *
+	 * @since 5.0.0
+	 * @var bool
+	 */
+	public $is_block_editor = false;
+
 	/**
 	 * Fetches a screen object.
 	 *
@@ -399,6 +407,22 @@ final class WP_Screen {
 		return ( $admin == $this->in_admin );
 	}
 
+	/**
+	 * Sets or returns whether the block editor is loading on the current screen.
+	 *
+	 * @since 5.0.0
+	 *
+	 * @param bool $set Optional. Sets whether the block editor is loading on the current screen or not.
+	 * @return bool True if the block editor is being loaded, false otherwise.
+	 */
+	public function is_block_editor( $set = null ) {
+		if ( $set !== null ) {
+			$this->is_block_editor = (bool) $set;
+		}
+
+		return $this->is_block_editor;
+	}
+
 	/**
 	 * Sets the old string-based contextual help for the screen for backward compatibility.
 	 *

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.0-alpha-43776';
+$wp_version = '5.0-alpha-43777';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.