update_engine: replace std::vector<char> with chromeos::Blob

To make update engine consistent with the rest of platform2 code
replaced std::vector<char> as the container of binary data with
chromeos::Blob.

BUG=None
TEST=`FEATURES=test emerge-link update_engine`

Change-Id: I6385fd2257d15aa24bfa74ac35512c2a06c33012
Reviewed-on: https://chromium-review.googlesource.com/247793
Reviewed-by: Gilad Arnold <[email protected]>
Reviewed-by: Alex Deymo <[email protected]>
Tested-by: Alex Vakulenko <[email protected]>
Commit-Queue: Alex Vakulenko <[email protected]>
diff --git a/download_action.cc b/download_action.cc
index 35b1174..6f55220 100644
--- a/download_action.cc
+++ b/download_action.cc
@@ -99,7 +99,7 @@
   return true;
 }
 
-void DownloadAction::WriteToP2PFile(const char *data,
+void DownloadAction::WriteToP2PFile(const void *data,
                                     size_t length,
                                     off_t file_offset) {
   if (p2p_sharing_fd_ == -1) {
@@ -248,8 +248,8 @@
 }
 
 void DownloadAction::ReceivedBytes(HttpFetcher *fetcher,
-                                   const char* bytes,
-                                   int length) {
+                                   const void* bytes,
+                                   size_t length) {
   // Note that bytes_received_ is the current offset.
   if (!p2p_file_id_.empty()) {
     WriteToP2PFile(bytes, length, bytes_received_);