Support multiple voices for all available modules (text-to-speech engines) on Linux.

This adds appropriate calls to retrieve voices from SpeechDispatcher and make it available through Chrome.

We combine all voices across all available modules into one list in order to conform to the way Chrome exposes voices.

Review URL: https://chromiumcodereview.appspot.com/15846006

git-svn-id: http://src.chromium.org/svn/trunk/src/build@202665 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

linux/system.gyp

@@ -520,6 +520,10 @@
                      'spd_set_notification_on',
                      'spd_set_voice_rate',
                      'spd_set_voice_pitch',
+                     'spd_list_synthesis_voices',
+                     'spd_set_synthesis_voice',
+                     'spd_list_modules',
+                     'spd_set_output_module',
           ],
           'message': 'Generating libspeechd library loader.',
           'process_outputs_as_sources': 1,