Adding an easy way to allow inline style attributes through sanitization

tools/dom/src/NodeValidatorBuilder.dart

Index: tools/dom/src/NodeValidatorBuilder.dart
diff --git a/tools/dom/src/NodeValidatorBuilder.dart b/tools/dom/src/NodeValidatorBuilder.dart
index c5f0c80542a90835393044215c1d36965ea7bdbf..41cab67cf9b140830fe4f3f189ecf9f6af5b1e85 100644
--- a/tools/dom/src/NodeValidatorBuilder.dart
+++ b/tools/dom/src/NodeValidatorBuilder.dart
@@ -110,6 +110,21 @@ class NodeValidatorBuilder implements NodeValidator {
   }
 
   /**
+   * Allow inline styles on elements.
+   *
+   * If [tagName] is not specified then this allows inline styles on all
+   * elements. Otherwise tagName limits the styles to the specified elements.
+   */
+  void allowInlineStyles({String tagName}) {
+    if (tagName == null) {
+      tagName = '*';
+    } else {
+      tagName = tagName.toUpperCase();
+    }
+    add(new _SimpleNodeValidator(null, allowedAttributes: ['$tagName::style']));
+  }
+
+  /**
    * Allow common safe HTML5 elements and attributes.
    *
    * This list is based off of the Caja whitelists at: