Add support for bsdiff of file system metadata blocks

delta_diff_generator.h

Index: delta_diff_generator.h
diff --git a/delta_diff_generator.h b/delta_diff_generator.h
index 50a3a89ed4d423fcd9b3a93ea3094cec3bb3bd27..e41aa58edf85cd2b98135a18d5c6862f55eea63f 100644
--- a/delta_diff_generator.h
+++ b/delta_diff_generator.h
@@ -103,6 +103,16 @@ class DeltaDiffGenerator {
                              DeltaArchiveManifest_InstallOperation* out_op,
                              bool gather_extents);
 
+  // Similar to ReadFileToDiff but instead of working with a regular file,
+  // this function processes all file system related metadata and adds the
+  // required operations to graph.
+  static bool DeltaReadMetadata(Graph* graph,
+                                std::vector<Block>* blocks,
+                                const std::string& old_image,
+                                const std::string& new_image,
+                                int data_fd,
+                                off_t* data_file_size);
+
   // Creates a dummy REPLACE_BZ node in the given |vertex|. This can be used
   // to provide scratch space. The node writes |num_blocks| blocks starting at
   // |start_block|The node should be marked invalid before writing all nodes to