Preliminary work on resuming downloads whose connections have expired.

base/file_util_win.cc

Index: base/file_util_win.cc
diff --git a/base/file_util_win.cc b/base/file_util_win.cc
index f538c20c4f847ae243873e65a333dc367bf9065a..03a76fb56763f7b799266cdffebcfed21fd5f752 100644
--- a/base/file_util_win.cc
+++ b/base/file_util_win.cc
@@ -200,9 +200,18 @@ bool ReplaceFile(const FilePath& from_path, const FilePath& to_path) {
     ::CloseHandle(target_file);
   // When writing to a network share, we may not be able to change the ACLs.
   // Ignore ACL errors then (REPLACEFILE_IGNORE_MERGE_ERRORS).
-  return ::ReplaceFile(to_path.value().c_str(),
+  BOOL replaced = ::ReplaceFile(to_path.value().c_str(),
       from_path.value().c_str(), NULL,
-      REPLACEFILE_IGNORE_MERGE_ERRORS, NULL, NULL) ? true : false;
+      REPLACEFILE_IGNORE_MERGE_ERRORS, NULL, NULL);
+
+  if (!replaced) {
+    DWORD replace_error = ::GetLastError();
+    DLOG(WARNING) << "Unable to replace file \"" << from_path.value()
+                  << "\" with \"" << to_path.value()
+                  << "\", error = " << replace_error
+                  << " (" << win_util::FormatMessage(replace_error) << ")";
+  }
+  return replaced ? true : false;
 }
 
 bool CopyFile(const FilePath& from_path, const FilePath& to_path) {