Add definition of window.speechSynthesis for cast

This is used by Chromevox.

Bug: b/110195060
Test: manual
Change-Id: I9e22aacf0c3335d70eb92ea9b66f6e11a7ef2f7c
Reviewed-on: https://chromium-review.googlesource.com/1105028
Commit-Queue: Kevin Schoedel <kpschoedel@chromium.org>
Reviewed-by: Alex Sakhartchouk <alexst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568493}

chromecast/renderer/cast_extensions_dispatcher_delegate.cc

@@ -73,6 +73,7 @@ void CastExtensionsDispatcherDelegate::PopulateSourceMap(
   source_map->RegisterSource("automationEvent", IDR_AUTOMATION_EVENT_JS);
   source_map->RegisterSource("automationNode", IDR_AUTOMATION_NODE_JS);
   source_map->RegisterSource("tabs", IDR_TABS_CUSTOM_BINDINGS_JS);
+  source_map->RegisterSource("automationNode", IDR_SPEECH_SYNTHESIS_JS);
 }
 
 void CastExtensionsDispatcherDelegate::RequireAdditionalModules(

chromecast/renderer/resources/extensions/speech_synthesis.js

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Imported from //chrome/browser/resources/chromeos/select_to_speak/externs.js
+
+window.speechSynthesis = {};

chromecast/renderer/resources/extensions_renderer_resources.grd

@@ -14,6 +14,7 @@
       <include name="IDR_AUTOMATION_NODE_JS" file="extensions\automation\automation_node.js" type="BINDATA" />
       <include name="IDR_TABS_CUSTOM_BINDINGS_JS" file="extensions\tabs_custom_bindings.js" type="BINDATA" />
       <include name="IDR_TTS_CUSTOM_BINDINGS_JS" file="extensions\tts_custom_bindings.js" type="BINDATA" />
+      <include name="IDR_SPEECH_SYNTHESIS_JS" file="extensions\speech_synthesis.js" type="BINDATA" />
     </includes>
   </release>
 </grit>