Move Mime type handling to streamsPrivate API, so that it works on Desktop Chrome.

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 9a8d6347ab903a6311930ab8bf667ecb15e0987b..41734145ca85e49e253b78797e60841aba33847a 100644
--- a/chrome/common/extensions/extension_constants.h
+++ b/chrome/common/extensions/extension_constants.h
@@ -117,6 +117,9 @@ namespace extension_misc {
   // The extension id of the Office Viewer dev extension.
   extern const char kQuickOfficeDevExtensionId[];
 
+  // The extension id used for testing streamsPrivate
+  extern const char kStreamsPrivateTestExtensionId[];
+
   // The extension id of the Web Store component application.
   extern const char kWebStoreAppId[];