add options page and preserve code setting.

src/options.js

@@ -0,0 +1,28 @@
+// Restores preferences from chrome.storage.
+function restoreOptions() {
+	chrome.storage.sync.get({
+		preserveLastCode: true
+	}, function(items) {
+		document.forms.optionsForm.preserveLastCode.checked = items.preserveLastCode;
+	});
+}
+
+function saveOptions(e) {
+	var preserveLastCode = document.forms.optionsForm.preserveLastCode.checked;
+
+	chrome.storage.sync.set({
+		preserveLastCode: preserveLastCode
+	}, function() {
+		var status = document.getElementById('js-status');
+		status.textContent = 'Settings saved.';
+		setTimeout(function() {
+			status.textContent = '';
+		}, 750);
+	});
+
+	e.preventDefault();
+}
+
+document.addEventListener('DOMContentLoaded', restoreOptions);
+document.forms.optionsForm.addEventListener('submit',
+	saveOptions);