add missing externs to repo

externs/webextension_polyfill/manifest/ContentScript.hx

@@ -0,0 +1,57 @@
+package webextension_polyfill.manifest;
+
+/**
+	Details of the script or CSS to inject. Either the code or the file property must be set,
+	but both may not be set at the same time. Based on InjectDetails, but using underscore rather than camel case naming
+	conventions.
+**/
+typedef ContentScript = {
+	var matches : Array<String>;
+	/**
+		Optional.
+	**/
+	@:optional
+	var exclude_matches : Array<String>;
+	/**
+		Optional.
+	**/
+	@:optional
+	var include_globs : Array<String>;
+	/**
+		Optional.
+	**/
+	@:optional
+	var exclude_globs : Array<String>;
+	/**
+		The list of CSS files to inject
+		Optional.
+	**/
+	@:optional
+	var css : Array<String>;
+	/**
+		The list of JS files to inject
+		Optional.
+	**/
+	@:optional
+	var js : Array<String>;
+	/**
+		If allFrames is <code>true</code>, implies that the JavaScript or CSS should be injected into all frames of current page.
+		By default, it's <code>false</code> and is only injected into the top frame.
+		Optional.
+	**/
+	@:optional
+	var all_frames : Bool;
+	/**
+		If matchAboutBlank is true, then the code is also injected in about:blank and about:srcdoc frames if your extension has
+		access to its parent document. Code cannot be inserted in top-level about:-frames. By default it is <code>false</code>.
+		Optional.
+	**/
+	@:optional
+	var match_about_blank : Bool;
+	/**
+		The soonest that the JavaScript or CSS will be injected into the tab. Defaults to "document_idle".
+		Optional.
+	**/
+	@:optional
+	var run_at : webextension_polyfill.extensiontypes.RunAt;
+};