Set Content-Type header for ?format=TEXT content replies on paths

HTTP servers should always send a Content-Type response header to
prevent browsers from entering into (a possibly stupid) sniffing
mode. Since the payload is wrapped up in base64 this is really a
text/plain reply.

Using the two-arg form of startRenderText() will send a text/plain
Content-Type, which is exactly correct here.

Change-Id: I194a1446c62e4409c27e8fc72aa43846ea3438a9

gitiles-servlet/src/main/java/com/google/gitiles/PathServlet.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/PathServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/PathServlet.java
index ff660b8..ecde06a 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/PathServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/PathServlet.java
@@ -208,7 +208,7 @@
   private void writeBlobText(HttpServletRequest req, HttpServletResponse res, WalkResult wr)
       throws IOException {
     setModeHeader(res, wr.type);
-    try (Writer writer = startRenderText(req, res, null);
+    try (Writer writer = startRenderText(req, res);
         OutputStream out = BaseEncoding.base64().encodingStream(writer)) {
       wr.getObjectReader().open(wr.id).copyTo(out);
     }
@@ -218,7 +218,7 @@
       throws IOException {
     setModeHeader(res, wr.type);
 
-    try (Writer writer = startRenderText(req, res, null);
+    try (Writer writer = startRenderText(req, res);
         OutputStream out = BaseEncoding.base64().encodingStream(writer)) {
       // Match git ls-tree format.
       while (wr.tw.next()) {