Add support for new "removed" API flag.

The removed flag is informational only: it has no effect on runtime
behaviour, so all we need to do here is to recognize it as a valid
flag so it doesn't cause problems.

Bug: 171300342
Test: m
Change-Id: I6bb469410c6728e1cc2860f5441b8021c3a80205
diff --git a/libartbase/base/hiddenapi_stubs.h b/libartbase/base/hiddenapi_stubs.h
index 94ef95c..ccfbc42 100644
--- a/libartbase/base/hiddenapi_stubs.h
+++ b/libartbase/base/hiddenapi_stubs.h
@@ -47,7 +47,8 @@
 
   static bool IsStubsFlag(const std::string_view& api_flag_name) {
     return api_flag_name == kPublicApiStr || api_flag_name == kSystemApiStr ||
-        api_flag_name == kTestApiStr || api_flag_name == kCorePlatformApiStr;
+        api_flag_name == kTestApiStr || api_flag_name == kCorePlatformApiStr ||
+        api_flag_name == kRemovedApiStr;
   }
 
  private:
@@ -55,6 +56,7 @@
   static constexpr std::string_view kSystemApiStr{"system-api"};
   static constexpr std::string_view kTestApiStr{"test-api"};
   static constexpr std::string_view kCorePlatformApiStr{"core-platform-api"};
+  static constexpr std::string_view kRemovedApiStr{"removed"};
 };
 
 }  // namespace hiddenapi