Add lz4diff patch routines

Test: th
Bug: 206729162

Change-Id: I76a404e233e7683812bac65520c6c065e9a1ffe2
diff --git a/common/utils.h b/common/utils.h
index a0a466d..46e41f0 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -312,6 +312,12 @@
                  ssize_t out_data_size,
                  size_t block_size);
 
+bool ReadExtents(FileDescriptorPtr path,
+                 const std::vector<Extent>& extents,
+                 brillo::Blob* out_data,
+                 ssize_t out_data_size,
+                 size_t block_size);
+
 bool WriteExtents(const std::string& path,
                   const google::protobuf::RepeatedPtrField<Extent>& extents,
                   const brillo::Blob& data,
@@ -333,6 +339,11 @@
                  brillo::Blob* out_data,
                  size_t block_size);
 
+bool ReadExtents(FileDescriptorPtr path,
+                 const google::protobuf::RepeatedPtrField<Extent>& extents,
+                 brillo::Blob* out_data,
+                 size_t block_size);
+
 // Read the current boot identifier and store it in |boot_id|. This identifier
 // is constants during the same boot of the kernel and is regenerated after
 // reboot. Returns whether it succeeded getting the boot_id.