code: public static SourceSnippet callChildGetter(final GinjectorBindings childBindings,
        final Key<?> key) {
      return new SourceSnippet() {
        public String getSource(InjectorWriteContext writeContext) {
          return writeContext.callChildGetter(childBindings, key);
        }
      };
    }
docs: Creates a snippet that evaluates to an injected instance of the given key,
  as produced by the given child.