Add a separate protector UMA state when backup is overwritten by migration.

chrome/browser/webdata/keyword_table.h

Index: chrome/browser/webdata/keyword_table.h
diff --git a/chrome/browser/webdata/keyword_table.h b/chrome/browser/webdata/keyword_table.h
index 56f544370f8e9e9979d52d61409218605d95604c..facdf5f02c37dc7677a6e42b05056a7d3854acb1 100644
--- a/chrome/browser/webdata/keyword_table.h
+++ b/chrome/browser/webdata/keyword_table.h
@@ -93,8 +93,7 @@ class KeywordTable : public WebDatabaseTable {
   // Comma-separated list of keyword table column names, in order.
   static const char kKeywordColumns[];
 
-  KeywordTable(sql::Connection* db, sql::MetaTable* meta_table)
-      : WebDatabaseTable(db, meta_table) {}
+  KeywordTable(sql::Connection* db, sql::MetaTable* meta_table);
   virtual ~KeywordTable();
   virtual bool Init() OVERRIDE;
   virtual bool IsSyncable() OVERRIDE;
@@ -199,6 +198,9 @@ class KeywordTable : public WebDatabaseTable {
   // "keywords_backup" from version 44 to version 45.
   bool MigrateKeywordsTableForVersion45(const std::string& name);
 
+  // Whether the backup was overwritten during migration.
+  bool backup_overwritten_;
+
   DISALLOW_COPY_AND_ASSIGN(KeywordTable);
 };