The mix of explicit vs. implicit dependency tracking is confusing. You have an explicit requirements.addConfigurationProperty(), but the @Source-file tracking is implicit via ResourceContext.getResourcesForMethod().
The SupportsGeneratorResourceCaching interface makes sense, but the HasFindableResourceDependencies smells. Would the HFRD interface be necessary if URL dependencies were tracked explicitly? Where's the escape hatch for staleness, say if an RG wanted to depend on an arbitrary external resource? http://gwt-code-reviews.appspot.com/1236801/show -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
