IMS: start and stop dtmf tones.

Support of start and stop dtmf tones in Imsphone

Bug: 18371919
Change-Id: I986f6b8e9aa1a5729d280eb8a5c60e129c3796cd
CRs-Fixed: 751797

telephony/java/com/android/ims/internal/IImsCallSession.aidl

@@ -222,6 +222,20 @@ interface IImsCallSession {
      */
     void sendDtmf(char c, in Message result);
 
+    /**
+     * Start a DTMF code. According to <a href="http://tools.ietf.org/html/rfc2833">RFC 2833</a>,
+     * event 0 ~ 9 maps to decimal value 0 ~ 9, '*' to 10, '#' to 11, event 'A' ~ 'D' to 12 ~ 15,
+     * and event flash to 16. Currently, event flash is not supported.
+     *
+     * @param c the DTMF to send. '0' ~ '9', 'A' ~ 'D', '*', '#' are valid inputs.
+     */
+    void startDtmf(char c);
+
+    /**
+     * Stop a DTMF code.
+     */
+    void stopDtmf();
+
     /**
      * Sends an USSD message.
      *