Add Notification images (Blink + desktop implementation)

content/public/common/platform_notification_data.h

Index: content/public/common/platform_notification_data.h
diff --git a/content/public/common/platform_notification_data.h b/content/public/common/platform_notification_data.h
index 97f723493f75a4ee8d3bbc26650a0a50b29155c0..a2108d0b4b9084b67097d6a707cfa7775fe47b69 100644
--- a/content/public/common/platform_notification_data.h
+++ b/content/public/common/platform_notification_data.h
@@ -83,6 +83,10 @@ struct CONTENT_EXPORT PlatformNotificationData {
   // tag will replace the first displayed notification.
   std::string tag;
 
+  // URL of the image contents of the notification. May be empty if no url was
+  // specified.
+  GURL image;
+
   // URL of the icon which is to be displayed with the notification.
   GURL icon;