Make it easier and more efficient to use trusted HTML text

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index 5ab6241ee4e47d93cb7c2ca1fae7ac7e4579d59b..1de3e1cc28e3865a0fea7f8051e264284cb7a318 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -12423,8 +12423,12 @@ abstract class Element extends Node implements GlobalEventHandlers, ParentNode,
    */
   void insertAdjacentHtml(String where, String html, {NodeValidator validator,
       NodeTreeSanitizer treeSanitizer}) {
-      _insertAdjacentNode(where, new DocumentFragment.html(html,
-          validator: validator, treeSanitizer: treeSanitizer));
+      if (treeSanitizer is _TrustedHtmlTreeSanitizer) {
+        _insertAdjacentHtml(where, html);
+      } else {
+        _insertAdjacentNode(where, new DocumentFragment.html(html,
+            validator: validator, treeSanitizer: treeSanitizer));
+      }
   }
 
 
@@ -12695,8 +12699,12 @@ abstract class Element extends Node implements GlobalEventHandlers, ParentNode,
   void setInnerHtml(String html,
     {NodeValidator validator, NodeTreeSanitizer treeSanitizer}) {
     text = null;
-    append(createFragment(
-        html, validator: validator, treeSanitizer: treeSanitizer));
+    if (treeSanitizer is _TrustedHtmlTreeSanitizer) {
+      _innerHtml = html;
+    } else {
+      append(createFragment(
+          html, validator: validator, treeSanitizer: treeSanitizer));
+    }
   }
   String get innerHtml => _innerHtml;
 
@@ -40622,9 +40630,27 @@ abstract class NodeTreeSanitizer {
    * will mark the entire tree as unsafe.
    */
   void sanitizeTree(Node node);
+
+  /**
+   * A sanitizer for trees that we trust. It does no validation and allows
+   * any elements. It is also more efficient, since it can pass the text
+   * directly through to the underlying APIs without creating a document 
+   * fragment to be sanitized.
+   */
+  static const trusted = const _TrustedHtmlTreeSanitizer();
 }
 
 /**
+ * A sanitizer for trees that we trust. It does no validation and allows
+ * any elements.
+ */
+class _TrustedHtmlTreeSanitizer implements NodeTreeSanitizer {
+  const _TrustedHtmlTreeSanitizer();
+
+  sanitizeTree(Node node) {}
+}
+  
+/**
  * Defines the policy for what types of uris are allowed for particular
  * attribute values.
  *