AU: When applying delta locally, get source checksums

When applying a delta on the host, we need to calculate the original
checksums for the rootfs/kernel for the delta performer. This CL does
that.

Also:
- Log old/new checksums in performer
- Add base64 encode function to OmahaHashCalculator

BUG=8062
TEST=unittests; applied delta on host

Review URL: http://codereview.chromium.org/4042004

Change-Id: I953d7dd34cb65269e9b44e22c87a13a7f52e66d4
diff --git a/delta_diff_generator.h b/delta_diff_generator.h
index 9fbe0a5..3156fd6 100644
--- a/delta_diff_generator.h
+++ b/delta_diff_generator.h
@@ -215,6 +215,10 @@
   // (e.g., a move operation that copies blocks onto themselves).
   static bool IsNoopOperation(const DeltaArchiveManifest_InstallOperation& op);
 
+  static bool InitializePartitionInfo(bool is_kernel,
+                                      const std::string& partition,
+                                      PartitionInfo* info);
+
  private:
   // This should never be constructed
   DISALLOW_IMPLICIT_CONSTRUCTORS(DeltaDiffGenerator);