Identity API: Change WebAuthFlow to use <webview> instead of a normal browser pop-up.

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 9566f17952f28875d5bef2fad2a3f337f7fbf028..ef2022f3dc0b743fcbe4460780ae12bb43a77d9c 100644
--- a/chrome/common/extensions/extension_constants.h
+++ b/chrome/common/extensions/extension_constants.h
@@ -160,6 +160,9 @@ namespace extension_misc {
   // The extension id of the Youtube application.
   extern const char kYoutubeAppId[];
 
+  // The extension id of the Identity API UI application.
+  extern const char kIdentityApiUiAppId[];
+
   // Note: this structure is an ASN.1 which encodes the algorithm used
   // with its parameters. This is defined in PKCS #1 v2.1 (RFC 3447).
   // It is encoding: { OID sha1WithRSAEncryption      PARAMETERS NULL }