Generate all extension schema namespaces as "api" and instead vary the generated bundle names.

extensions/browser/api/cast_channel/cast_message_util.cc

Index: extensions/browser/api/cast_channel/cast_message_util.cc
diff --git a/extensions/browser/api/cast_channel/cast_message_util.cc b/extensions/browser/api/cast_channel/cast_message_util.cc
index 0bb1fb75b5fc5050b00912200d575456cca19fad..c2ddcf029ca7362e6432fa5d0303b32f3897691c 100644
--- a/extensions/browser/api/cast_channel/cast_message_util.cc
+++ b/extensions/browser/api/cast_channel/cast_message_util.cc
@@ -20,7 +20,7 @@ static const char kPlatformReceiverId[] = "receiver-0";
 }  // namespace
 
 namespace extensions {
-namespace core_api {
+namespace api {
 namespace cast_channel {
 
 bool MessageInfoToCastMessage(const MessageInfo& message,
@@ -157,5 +157,5 @@ bool IsAuthMessage(const CastMessage& message) {
 }
 
 }  // namespace cast_channel
-}  // namespace core_api
+}  // namespace api
 }  // namespace extensions