Updating MutationObserver.observe documentation.

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 f07da5cd9c18178f8df03a5ee0e272db51b4c126..81d125a22837f48caf687e971f67d2392eca6311 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -18598,6 +18598,16 @@ class MutationObserver extends NativeFieldWrapperClass2 {
     return true;
   }
 
+  /**
+   * Observes the target for the specified changes.
+   *
+   * Some requirements for the optional parameters:
+   *
+   * * Either childList, attributes or characterData must be true.
+   * * If attributeOldValue is true then attributes must also be true.
+   * * If attributeFilter is specified then attributes must be true.
+   * * If characterDataOldValue is true then characterData must be true.
+   */
   void observe(Node target,
                {bool childList,
                 bool attributes,