fix a few more codegen issues:

lib/src/js/builder.dart

Index: lib/src/js/builder.dart
diff --git a/lib/src/js/builder.dart b/lib/src/js/builder.dart
index f215da214a6795ed463467790084834a2988e91d..affcffea42abfd1fce7a66b1907516ee87968bb1 100644
--- a/lib/src/js/builder.dart
+++ b/lib/src/js/builder.dart
@@ -298,17 +298,25 @@ class JsBuilder {
   LiteralString escapedString(String value, [String quote = '"']) {
    // Start by escaping the backslashes.
     String escaped = value.replaceAll('\\', '\\\\');
-    // Do not escape unicode characters and ' because they are allowed in the
-    // string literal anyway.
-    var re = new RegExp('\n|\r|$quote|\b|\f|\t|\v');
+
+    // http://www.ecma-international.org/ecma-262/6.0/#sec-literals-string-literals
+    // > All code points may appear literally in a string literal except for the
+    // > closing quote code points, U+005C (REVERSE SOLIDUS),
+    // > U+000D (CARRIAGE RETURN), U+2028 (LINE SEPARATOR),
+    // > U+2029 (PARAGRAPH SEPARATOR), and U+000A (LINE FEED).
+    var re = new RegExp('\n|\r|$quote|\b|\f|\t|\v|\u2028|\u2029');
     escaped = escaped.replaceAllMapped(re, (m) {
       switch (m.group(0)) {
         case "\n" : return r"\n";
         case "\r" : return r"\r";
+        case "\u2028": return r"\u2028";
+        case "\u2029": return r"\u2029";
         // Quotes are only replaced if they conflict with the containing quote
         case '"':   return r'\"';
         case "'":   return r"\'";
         case "`":   return r"\`";
+        // TODO(jmesserly): these don't need to be escaped for correctness,
+        // but they are conventionally escaped.
         case "\b" : return r"\b";
         case "\t" : return r"\t";
         case "\f" : return r"\f";