Add test and some docs for bug 376660. r=biesi

netwerk/base/public/nsIUnicharStreamLoader.idl

@@ -54,6 +54,9 @@ interface nsIUnicharStreamLoaderObserver : nsISupports
    * @param aLength the length of aFirstSegment
    *
    * @return charset corresponding to this stream
+   *
+   * @note this method will only be called if the stream loader receives an
+   *       OnDataAvailable call.
    */
   ACString onDetermineCharset(in nsIUnicharStreamLoader aLoader,
                               in nsISupports aContext,
@@ -72,6 +75,9 @@ interface nsIUnicharStreamLoaderObserver : nsISupports
    * This method will always be called asynchronously by the
    * nsUnicharIStreamLoader involved, on the thread that called the
    * loader's init() method.
+   *
+   * @note If the stream loader does not receive an OnDataAvailable call,
+   *       aUnicharData will be null, and aStatus will be a success value.
    */
   void onStreamComplete(in nsIUnicharStreamLoader aLoader,
                         in nsISupports aContext,

netwerk/test/unit/test_bug376660.js

@@ -0,0 +1,37 @@
+var Cc = Components.classes;
+var Ci = Components.interfaces;
+
+var listener = {
+  QueryInterface: function listener_qi(iid) {
+    if (iid.equals(Ci.nsISupports) ||
+        iid.equals(Ci.nsIUnicharStreamLoaderObserver)) {
+      return this;
+    }
+    throw Components.results.NS_ERROR_NO_INTERFACE;
+  },
+  onDetermineCharset : function onDetermineCharset(loader, context,
+                                                   data, length)
+  {
+    return "us-ascii";
+  },
+  onStreamComplete : function onStreamComplete (loader, context, status, data)
+  {
+    do_check_eq(status, Components.results.NS_OK);
+    do_check_eq(data, null);
+    do_check_neq(loader.channel, null);
+    do_test_finished();
+  }
+};
+
+function run_test() {
+  var f =
+      Cc["@mozilla.org/network/unichar-stream-loader;1"].
+      createInstance(Ci.nsIUnicharStreamLoader);
+  f.init(listener, 4096);
+
+  var ios = Components.classes["@mozilla.org/network/io-service;1"]
+                      .getService(Components.interfaces.nsIIOService);
+  var chan = ios.newChannel("data:text/plain,", null, null);
+  chan.asyncOpen(f, null);
+  do_test_pending();
+}