AU: Some graph types and a couple utility functions

These will be used by the delta diff generator.

Review URL: http://codereview.chromium.org/578009
diff --git a/SConstruct b/SConstruct
index 38ae3f1..0f600a2 100644
--- a/SConstruct
+++ b/SConstruct
@@ -93,6 +93,7 @@
                    filesystem_copier_action.cc
                    filesystem_iterator.cc
                    file_writer.cc
+                   graph_utils.cc
                    gzip.cc
                    libcurl_http_fetcher.cc
                    omaha_hash_calculator.cc
@@ -117,6 +118,7 @@
                             file_writer_unittest.cc
                             filesystem_copier_action_unittest.cc
                             filesystem_iterator_unittest.cc
+                            graph_utils_unittest.cc
                             gzip_unittest.cc
                             http_fetcher_unittest.cc
                             mock_http_fetcher.cc