Implement offline mode behind a flag

net/http/http_cache_transaction.cc

Index: net/http/http_cache_transaction.cc
diff --git a/net/http/http_cache_transaction.cc b/net/http/http_cache_transaction.cc
index 491f2f39345013eeb2508d8b30942fc3cbabb2d9..c4dfa7b2fe60340cf1ac254e930c6a60fe943365 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -884,6 +884,9 @@ int HttpCache::Transaction::DoSuccessfulSendRequest() {
     next_state_ = STATE_SEND_REQUEST;
     return OK;
   }
+
+  response_.network_verified = true;
+
   if (handling_206_ && mode_ == READ_WRITE && !truncated_ && !is_sparse_) {
     // We have stored the full entry, but it changed and the server is
     // sending a range. We have to delete the old entry.