Add the ability to show a plugin icon on the "Dashboard -> Updates" p…

…age.

Usage: Add the following entry to your JSON file:

"icons" : {
	"1x" : "http://example.com/assets/icon-128x128.png",
	"2x" : "http://example.com/assets/icon-256x256.png",
	"svg": "http://example.com/assets/icon.svg"
} 

All of the keys are optional. They should point to different versions of the same icon:
- "1x": a 128x128 px image.
- "2x": a 256x256 px image for HiDPI screens.
- "svg": a vector version of the icon.

See WordPress.org for more information on supported icon sizes and image formats:  
https://developer.wordpress.org/plugins/wordpress-org/plugin-assets/#plugin-icons

Suggested in #153

Puc/v4p3/Plugin/Info.php

@@ -16,9 +16,11 @@ class Puc_v4p3_Plugin_Info extends Puc_v4p3_Metadata {
 		public $version;
 		public $homepage;
 		public $sections = array();
+		public $download_url;
+
 		public $banners;
+		public $icons = array();
 		public $translations = array();
-		public $download_url;
 
 		public $author;
 		public $author_homepage;
@@ -51,8 +53,9 @@ public static function fromJson($json){
 				return null;
 			}
 
-			//json_decode decodes assoc. arrays as objects. We want it as an array.
+			//json_decode decodes assoc. arrays as objects. We want them as arrays.
 			$instance->sections = (array)$instance->sections;
+			$instance->icons = (array)$instance->icons;
 
 			return $instance;
 		}

Puc/v4p3/Plugin/Update.php

@@ -13,10 +13,11 @@ class Puc_v4p3_Plugin_Update extends Puc_v4p3_Update {
 		public $homepage;
 		public $upgrade_notice;
 		public $tested;
+		public $icons = array();
 		public $filename; //Plugin filename relative to the plugins directory.
 
 		protected static $extraFields = array(
-			'id', 'homepage', 'tested', 'upgrade_notice', 'filename',
+			'id', 'homepage', 'tested', 'upgrade_notice', 'icons', 'filename',
 		);
 
 		/**
@@ -72,18 +73,36 @@ protected function getFieldNames() {
 		 *
 		 * @return object
 		 */
-		public function toWpFormat(){
+		public function toWpFormat() {
 			$update = parent::toWpFormat();
 
 			$update->id = $this->id;
 			$update->url = $this->homepage;
 			$update->tested = $this->tested;
 			$update->plugin = $this->filename;
 
-			if ( !empty($this->upgrade_notice) ){
+			if ( !empty($this->upgrade_notice) ) {
 				$update->upgrade_notice = $this->upgrade_notice;
 			}
 
+			if ( !empty($this->icons) && is_array($this->icons) ) {
+				//This should be an array with up to 4 keys: 'svg', '1x', '2x' and 'default'.
+				//Docs: https://developer.wordpress.org/plugins/wordpress-org/plugin-assets/#plugin-icons
+				$icons = array_intersect_key(
+					$this->icons,
+					array('svg' => true, '1x' => true, '2x' => true, 'default' => true)
+				);
+				if ( !empty($icons) ) {
+					$update->icons = $icons;
+
+					//It appears that the 'default' icon isn't used anywhere in WordPress 4.9,
+					//but lets set it just in case a future release needs it.
+					if ( !isset($update->icons['default']) ) {
+						$update->icons['default'] = current($update->icons);
+					}
+				}
+			}
+
 			return $update;
 		}
 	}

examples/plugin.json

@@ -18,6 +18,11 @@
 		"changelog": "(Recommended) Changelog. <p>This section will be displayed by default when the user clicks 'View version x.y.z details'.</p>",
 		"custom_section": "This is a custom section labeled 'Custom Section'."
 	},
+
+	"icons" : {
+		"1x" : "http://w-shadow.com/files/external-update-example/assets/icon-128x128.png",
+		"2x" : "http://w-shadow.com/files/external-update-example/assets/icon-256x256.png"
+    },
 
 	"banners": {
 		"low": "http://w-shadow.com/files/external-update-example/assets/banner-772x250.png",