RunSpeech Dispatcher in multi threaded mode.

When run in multi threaded mode, Speech Dispatcher notifies Chrome of significant tts events such as the end of a text utterance. This fixes some long standing issues with users of the tts api such as ChromeVox. Since speechd is indefinitely behind a flag, this change a no real impact except for users who explicitly want speechd.

TEST=run Chrome with speechd enabled, and observe ChromeVox receives end callbacks.

Review URL: https://codereview.chromium.org/1134223003

Cr-Commit-Position: refs/heads/master@{#329434}

chrome/browser/speech/tts_linux.cc

@@ -116,7 +116,7 @@ void TtsPlatformImplLinux::Initialize() {
     // http://crbug.com/317360
     ANNOTATE_SCOPED_MEMORY_LEAK;
     conn_ = libspeechd_loader_.spd_open(
-        "chrome", "extension_api", NULL, SPD_MODE_SINGLE);
+        "chrome", "extension_api", NULL, SPD_MODE_THREADED);
   }
   if (!conn_)
     return;
@@ -151,7 +151,7 @@ void TtsPlatformImplLinux::Reset() {
   if (conn_)
     libspeechd_loader_.spd_close(conn_);
   conn_ = libspeechd_loader_.spd_open(
-      "chrome", "extension_api", NULL, SPD_MODE_SINGLE);
+      "chrome", "extension_api", NULL, SPD_MODE_THREADED);
 }
 
 bool TtsPlatformImplLinux::PlatformImplAvailable() {