Add SafeHtml.asis to prevent escaping existing HTML text

This can be useful when reading constants from a constants file,
but its risky as the text is not escaped.

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/src/main/java/com/google/gwtexpui/safehtml/client/SafeHtml.java b/src/main/java/com/google/gwtexpui/safehtml/client/SafeHtml.java
index af7602f..7bdd0db 100644
--- a/src/main/java/com/google/gwtexpui/safehtml/client/SafeHtml.java
+++ b/src/main/java/com/google/gwtexpui/safehtml/client/SafeHtml.java
@@ -29,6 +29,11 @@
     return new SafeHtmlString(t.getHTML());
   }
 
+  /** @return the existing HTML text, wrapped in a safe buffer. */
+  public static SafeHtml asis(final String htmlText) {
+    return new SafeHtmlString(htmlText);
+  }
+
   /** Set the HTML property of a widget. */
   public static <T extends HasHTML> T set(final T e, final SafeHtml str) {
     e.setHTML(str.asString());