Make sanitizer tests handle IE11, where tagName can't be clobbered

tools/dom/src/Validators.dart

Index: tools/dom/src/Validators.dart
diff --git a/tools/dom/src/Validators.dart b/tools/dom/src/Validators.dart
index 60d8f35f654ae6320fde3a73cf3c9280566b769b..fd00bb971d4fd4eb29af41e0163227b9283da4d3 100644
--- a/tools/dom/src/Validators.dart
+++ b/tools/dom/src/Validators.dart
@@ -198,6 +198,9 @@ class _ValidatingTreeSanitizer implements NodeTreeSanitizer {
     var elementTagName = 'element tag unavailable';
     try {
       elementTagName = element.tagName;
+      if (elementTagName != elementTagName.toString() {

[sra1, 2015/05/27 00:45:18]

1. Parse error - missing ')'.
2. A malicious toString could return 'this'.
3. With --trust-type-annotations or type inference, this could plausibly be
optimized to a null check or `false`.

If you are really checking for a String, use
   if (confuse(elementTagName) is !String) {
     corrupted = true;
   }

[Alan Knight, 2015/05/27 19:54:47]

OK, this doesn't seem worthwhile, took it out.

+        corrupted = true; // The tag name is not a string
+      }
     } catch(e) {}
     _sanitizeElement(element, parent, corrupted, elementText, elementTagName,
         attrs, isAttr);
@@ -253,7 +256,7 @@ class _ValidatingTreeSanitizer implements NodeTreeSanitizer {
   void sanitizeNode(Node node, Node parent) {
     switch (node.nodeType) {
       case Node.ELEMENT_NODE:
-        _sanitizeUntrustedElement(node, parent); 
+        _sanitizeUntrustedElement(node, parent);
         break;
       case Node.COMMENT_NODE:
       case Node.DOCUMENT_FRAGMENT_NODE: