add missing externs to repo

externs/webextension_polyfill/storage/SyncStorageAreaSync.hx

@@ -0,0 +1,59 @@
+package webextension_polyfill.storage;
+
+typedef SyncStorageAreaSync = {
+	/**
+		The maximum total amount (in bytes) of data that can be stored in sync storage, as measured by the JSON stringification
+		of every value plus every key's length. Updates that would cause this limit to be exceeded fail immediately and set
+		$(ref:runtime.lastError).
+	**/
+	var QUOTA_BYTES : Int;
+	/**
+		The maximum size (in bytes) of each individual item in sync storage, as measured by the JSON stringification of its
+		value plus its key length. Updates containing items larger than this limit will fail immediately and set $(ref:runtime.
+		lastError).
+	**/
+	var QUOTA_BYTES_PER_ITEM : Int;
+	/**
+		The maximum number of items that can be stored in sync storage. Updates that would cause this limit to be exceeded will
+		fail immediately and set $(ref:runtime.lastError).
+	**/
+	var MAX_ITEMS : Int;
+	/**
+		<p>The maximum number of <code>set</code>, <code>remove</code>, or <code>clear</code>
+		operations that can be performed each hour. This is 1 every 2 seconds, a lower ceiling than the short term higher
+		writes-per-minute limit.</p><p>Updates that would cause this limit to be exceeded fail immediately and set $(ref:runtime.
+		lastError).</p>
+	**/
+	var MAX_WRITE_OPERATIONS_PER_HOUR : Int;
+	/**
+		<p>The maximum number of <code>set</code>, <code>remove</code>, or <code>clear</code>
+		operations that can be performed each minute. This is 2 per second, providing higher throughput than writes-per-hour
+		over a shorter period of time.</p><p>Updates that would cause this limit to be exceeded fail immediately and set
+		$(ref:runtime.lastError).</p>
+	**/
+	var MAX_WRITE_OPERATIONS_PER_MINUTE : Int;
+	/**
+		Gets one or more items from storage.
+	**/
+	function get(?keys:ts.AnyOf3<String, Array<String>, haxe.DynamicAccess<Dynamic>>):js.lib.Promise<haxe.DynamicAccess<Dynamic>>;
+	/**
+		Gets the amount of space (in bytes) being used by one or more items.
+	**/
+	function getBytesInUse(?keys:ts.AnyOf2<String, Array<String>>):js.lib.Promise<Float>;
+	/**
+		Sets multiple items.
+	**/
+	function set(items:haxe.DynamicAccess<Dynamic>):js.lib.Promise<ts.Undefined>;
+	/**
+		Removes one or more items from storage.
+	**/
+	function remove(keys:ts.AnyOf2<String, Array<String>>):js.lib.Promise<ts.Undefined>;
+	/**
+		Removes all items from storage.
+	**/
+	function clear():js.lib.Promise<ts.Undefined>;
+	/**
+		Fired when one or more items change.
+	**/
+	var onChanged : webextension_polyfill.events.Event<(changes:StorageAreaSyncOnChangedChangesType) -> Void>;
+};