GWTP creates the ginjector automagically with all its presenters and views getters. it also supports extending this ginjector for non GWTP objects. here's how you do it:
a. define an interface, lets name it GinjectorExtensions in package some.package.client
package some.package.client;
public interface GinjectorExtensions {
//your objects here
MyConstants getMyConstants();
MyMessages MyMessages();
MyRequestFactory getRequestFactory();
}
b. Edit your GWT module xml file to include the following line (which tells GWTP to add your lines of code to it's autogen Ginjector):
<set-configuration-property name="gin.ginjector.extensions"
value="some.package.client.GinjectorExtensions"/>
Then you just @Inject your objects anywhere and everything should work as expected.
EDIT: after reviewing your code, just remove the "extends Ginjector" from ClientInjectorAdditional and everything should work.