Simplify Autofill Scanner semantics

chrome/browser/autofill/autofill_scanner.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_AUTOFILL_AUTOFILL_SCANNER_H_
 #define CHROME_BROWSER_AUTOFILL_AUTOFILL_SCANNER_H_
 #pragma once
 
 #include <vector>
 
@@ skipping 11 matching lines @@
   // Advances the cursor by one step, if possible.
   void Advance();
 
   // Returns the current field in the stream, or |NULL| if there are no more
   // fields in the stream.
   const AutofillField* Cursor() const;
 
   // Returns |true| if the cursor has reached the end of the stream.
   bool IsEnd() const;
 
-  // Returns the most recently saved cursor -- see also |SaveCursor()|.
+  // Restores the most recently saved cursor. See also |SaveCursor()|.
   void Rewind();
 
-  // Saves the current cursor position.  Multiple cursor positions can be saved,
-  // with stack ordering semantics.  See also |Rewind()|.
-  void SaveCursor();
+  // Repositions the cursor to the specified |index|. See also |SaveCursor()|.
+  void RewindTo(size_t index);
+
+  // Saves and returns the current cursor position. See also |Rewind()| and
+  // |RewindTo()|.
+  size_t SaveCursor();
 
  private:
   // Indicates the current position in the stream, represented as a vector.
   std::vector<const AutofillField*>::const_iterator cursor_;
 
-  // A stack of saved positions in the stream.
-  std::vector<std::vector<const AutofillField*>::const_iterator> saved_cursors_;
+  // The most recently saved cursor.
+  std::vector<const AutofillField*>::const_iterator saved_cursor_;
+
+  // The beginning pointer for the stream.
+  const std::vector<const AutofillField*>::const_iterator begin_;
 
   // The past-the-end pointer for the stream.
   const std::vector<const AutofillField*>::const_iterator end_;
 
   DISALLOW_COPY_AND_ASSIGN(AutofillScanner);
 };
 
 #endif  // CHROME_BROWSER_AUTOFILL_AUTOFILL_SCANNER_H_