Add a GetSignature() method to dbus::MessageReader.

dbus/message.h

Index: dbus/message.h
diff --git a/dbus/message.h b/dbus/message.h
index db3456acd0cd2aadb81fe76ed239f7de5bdc4b03..d29e5e46e89021ab11b60f18c92d73047ad21873 100644
--- a/dbus/message.h
+++ b/dbus/message.h
@@ -111,7 +111,7 @@ class CHROME_DBUS_EXPORT Message {
   std::string GetMember();
   std::string GetErrorName();
   std::string GetSender();
-  std::string GetSignature();
+  std::string GetDataSignature();
   // Gets the serial and reply serial numbers. Returns 0 if not set.
   uint32 GetSerial();
   uint32 GetReplySerial();
@@ -463,6 +463,11 @@ class CHROME_DBUS_EXPORT MessageReader {
   // end of the message.
   Message::DataType GetDataType();
 
+  // Get the DBus signature of the value at the current iterator position.
+  // An empty string will be returned if the iterator points to the end of
+  // the message.
+  std::string GetDataSignature();
+
  private:
   // Returns true if the data type at the current iterator position
   // matches the given D-Bus type, such as DBUS_TYPE_BYTE.