Add skeleton for select-to-speak component extension.

chrome/common/extensions/extension_constants.h

Index: chrome/common/extensions/extension_constants.h
diff --git a/chrome/common/extensions/extension_constants.h b/chrome/common/extensions/extension_constants.h
index ff4aaa59ea33b3aef786baca54c9208dca3bb0c1..77f25675513e4c10cfc49150898dd074e01a0839 100644
--- a/chrome/common/extensions/extension_constants.h
+++ b/chrome/common/extensions/extension_constants.h
@@ -198,6 +198,11 @@ extern const char kChromeVoxExtensionId[];
 // Path to preinstalled ChromeVox screen reader extension (relative to
 // |chrome::DIR_RESOURCES|).
 extern const char kChromeVoxExtensionPath[];
+// The extension id of the Select-to-speak extension.
+extern const char kSelectToSpeakExtensionId[];
+// Path to preinstalled Select-to-speak extension (relative to
+// |chrome::DIR_RESOURCES|).
+extern const char kSelectToSpeakExtensionPath[];
 // Name of the manifest file in an extension when a special manifest is used
 // for guest mode.
 extern const char kGuestManifestFilename[];