Add TH element support to SafeHtmlBuilder

Simple wrapper functions to support creating a <th> element.

Change-Id: Ife1a3816db9da864d438ea16360f846766a48fc1
diff --git a/gerrit-gwtexpui/src/main/java/com/google/gwtexpui/safehtml/client/SafeHtmlBuilder.java b/gerrit-gwtexpui/src/main/java/com/google/gwtexpui/safehtml/client/SafeHtmlBuilder.java
index f63b5d0..8ff99ee 100644
--- a/gerrit-gwtexpui/src/main/java/com/google/gwtexpui/safehtml/client/SafeHtmlBuilder.java
+++ b/gerrit-gwtexpui/src/main/java/com/google/gwtexpui/safehtml/client/SafeHtmlBuilder.java
@@ -318,6 +318,16 @@
     return closeElement("td");
   }
 
+  /** Append "&lt;th&gt;"; attributes may be set if needed */
+  public SafeHtmlBuilder openTh() {
+    return openElement("th");
+  }
+
+  /** Append "&lt;/th&gt;" */
+  public SafeHtmlBuilder closeTh() {
+    return closeElement("th");
+  }
+
   /** Append "&lt;div&gt;"; attributes may be set if needed */
   public SafeHtmlBuilder openDiv() {
     return openElement("div");