Use more single quotes in js_runtime

sdk/lib/_internal/js_runtime/lib/constant_map.dart

Index: sdk/lib/_internal/js_runtime/lib/constant_map.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/constant_map.dart b/sdk/lib/_internal/js_runtime/lib/constant_map.dart
index 618dc9604047bc255086c47c4a7e164be8688c6d..e127673d4fa9f4cab5916b77cfa167cc6bb0f16e 100644
--- a/sdk/lib/_internal/js_runtime/lib/constant_map.dart
+++ b/sdk/lib/_internal/js_runtime/lib/constant_map.dart
@@ -26,9 +26,9 @@ abstract class ConstantMap<K, V> implements Map<K, V> {
       int length = 0;
       for (var k in keys) {
         var v = other[k];
-        if (k != "__proto__") {
+        if (k != '__proto__') {
           if (!jsHasOwnProperty(object, k)) length++;
-          JS("void", "#[#] = #", object, k, v);
+          JS('void', '#[#] = #', object, k, v);
         } else {
           containsProto = true;
           protoValue = v;
@@ -53,7 +53,7 @@ abstract class ConstantMap<K, V> implements Map<K, V> {
   String toString() => Maps.mapToString(this);
 
   static _throwUnmodifiable() {
-    throw new UnsupportedError("Cannot modify unmodifiable Map");
+    throw new UnsupportedError('Cannot modify unmodifiable Map');
   }
 
   void operator []=(K key, V val) => _throwUnmodifiable();