Ensure RevTag is parsed before using its body

Ideally these methods in RevTag should be calling parseBody.  As a
stopgap, we can do it ourselves.

No visible change intended.  This is intended as preparation for
callers to be able to use setRetainBody(false).

Change-Id: I2e9e4d3550156ea5d77f5624ab35f3ab66bea6e5

java/com/google/gitiles/LogServlet.java

diff --git a/java/com/google/gitiles/LogServlet.java b/java/com/google/gitiles/LogServlet.java
index 0dd00f3..6982e0a 100644
--- a/java/com/google/gitiles/LogServlet.java
+++ b/java/com/google/gitiles/LogServlet.java
@@ -110,7 +110,7 @@
         List<Map<String, Object>> tags = Lists.newArrayListWithExpectedSize(1);
         for (RevObject o : RevisionServlet.listObjects(paginator.getWalk(), view.getRevision())) {
           if (o instanceof RevTag) {
-            tags.add(new TagSoyData(linkifier, req).toSoyData((RevTag) o, df));
+            tags.add(new TagSoyData(linkifier, req).toSoyData(paginator.getWalk(), (RevTag) o, df));
           }
         }
         if (!tags.isEmpty()) {