AU: Support signed payload verification through the delta generator.

The following command will verify a signed payload:

./delta_generator -in_file <payload> -public_key <key.pem>

Add a unit test for signature verification.

BUG=chromium-os:10936
TEST=unit tests

Change-Id: I3bb464608c22229141f9819b27503b6de778c495

Review URL: http://codereview.chromium.org/6271003
diff --git a/omaha_hash_calculator.h b/omaha_hash_calculator.h
index 762b8d4..9735ac8 100644
--- a/omaha_hash_calculator.h
+++ b/omaha_hash_calculator.h
@@ -60,6 +60,9 @@
   // success, and false otherwise.
   bool SetContext(const std::string& context);
 
+  static bool RawHashOfBytes(const char* data,
+                             size_t length,
+                             std::vector<char>* out_hash);
   static bool RawHashOfData(const std::vector<char>& data,
                             std::vector<char>* out_hash);
   static off_t RawHashOfFile(const std::string& name, off_t length,