This is a known issue: Chrome changed the way it deals with Source Maps and this lead to an incompatibility with how GWT produces them.
This is fixed in 2.5.1-rc1 that's just been published to Central (a couple days ago, not yet officially announced). See http://mojo.codehaus.org/gwt-maven-plugin/user-guide/using-different-gwt-sdk-version.html to use it into your build. I'll release a new version of the gwt-maven-plugin that "links" to this version, and then update the archetypes.