Convert string16 to base::string16 in content.

content/browser/indexed_db/indexed_db_index_writer.cc

Index: content/browser/indexed_db/indexed_db_index_writer.cc
diff --git a/content/browser/indexed_db/indexed_db_index_writer.cc b/content/browser/indexed_db/indexed_db_index_writer.cc
index 3b36cad0ec9355a71580774d354614d356f3674d..1c2ac0ab5a1b6ce62ba7eadc20fb6003676bf55e 100644
--- a/content/browser/indexed_db/indexed_db_index_writer.cc
+++ b/content/browser/indexed_db/indexed_db_index_writer.cc
@@ -34,7 +34,7 @@ bool IndexWriter::VerifyIndexKeys(
     int64 index_id,
     bool* can_add_keys,
     const IndexedDBKey& primary_key,
-    string16* error_message) const {
+    base::string16* error_message) const {
   *can_add_keys = false;
   for (size_t i = 0; i < index_keys_.size(); ++i) {
     bool ok = AddingKeyAllowed(backing_store,
@@ -122,7 +122,7 @@ bool MakeIndexWriters(
     const std::vector<int64>& index_ids,
     const std::vector<IndexedDBDatabase::IndexKeys>& index_keys,
     ScopedVector<IndexWriter>* index_writers,
-    string16* error_message,
+    base::string16* error_message,
     bool* completed) {
   DCHECK_EQ(index_ids.size(), index_keys.size());
   *completed = false;