AU: Add support for signing of update payloads after they're generated.

The change adds 2 methods -- one that takes an unsigned payload and a raw
signature size and returns the hash that needs to be signed, and another one
that takes an unsigned payload and a raw signature and generates the signed
payload.

BUG=chromium-os:10872
TEST=unit tests

Change-Id: I65bbe72a1ec67e603e78508c33893695b7de0e6a

Review URL: http://codereview.chromium.org/6265001
diff --git a/delta_diff_generator.h b/delta_diff_generator.h
index d02de48..79683e5 100644
--- a/delta_diff_generator.h
+++ b/delta_diff_generator.h
@@ -232,6 +232,12 @@
       Vertex::Index vertex,
       std::vector<DeltaDiffGenerator::Block>* blocks);
 
+  // Adds to |manifest| a dummy operation that points to a signature blob
+  // located at the specified offset/length.
+  static void AddSignatureOp(uint64_t signature_blob_offset,
+                             uint64_t signature_blob_length,
+                             DeltaArchiveManifest* manifest);
+
  private:
   // This should never be constructed
   DISALLOW_IMPLICIT_CONSTRUCTORS(DeltaDiffGenerator);