Implement lossy pref behavior for JsonPrefStore.

chrome/browser/spellchecker/spellcheck_custom_dictionary.cc

Index: chrome/browser/spellchecker/spellcheck_custom_dictionary.cc
diff --git a/chrome/browser/spellchecker/spellcheck_custom_dictionary.cc b/chrome/browser/spellchecker/spellcheck_custom_dictionary.cc
index f63a32bc953fa841337cb428b3f753e5b1c1bd00..e69fce80bc4b4c12c75f9650ba3fed7a1306ca56 100644
--- a/chrome/browser/spellchecker/spellcheck_custom_dictionary.cc
+++ b/chrome/browser/spellchecker/spellcheck_custom_dictionary.cc
@@ -120,7 +120,7 @@ void SaveDictionaryFileReliably(
   std::string checksum = base::MD5String(content.str());
   content << CHECKSUM_PREFIX << checksum;
   base::CopyFile(path, path.AddExtension(BACKUP_EXTENSION));
-  base::ImportantFileWriter::WriteFileAtomically(path, content.str());
+  base::ImportantFileWriterImpl::WriteFileAtomically(path, content.str());
 }
 
 // Removes duplicate and invalid words from |to_add| word list and sorts it.