Add text field change handling for autofill preview in textarea element.

public/web/WebFormControlElement.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 46 matching lines @@
     BLINK_EXPORT bool isEnabled() const;
     BLINK_EXPORT bool isReadOnly() const;
     BLINK_EXPORT WebString formControlName() const;
     BLINK_EXPORT WebString formControlType() const;
 
     BLINK_EXPORT void dispatchFormControlChangeEvent();
 
     BLINK_EXPORT bool isAutofilled() const;
     BLINK_EXPORT void setAutofilled(bool);
 
+    // This returns the non-sanitized, exact value inside the text input field
+    // or insisde the textarea. If neither input element nor textarea element,
+    // an empty string is returned.

[tkent, 2014/03/05 23:18:39]

Actually, *null* string is returned, not *empty* string.

+    BLINK_EXPORT WebString editingValue() const;
+
+    // The returned value represents a cursor/caret position at the current
+    // selection's start for text input field or textarea. If neither input
+    // element nor textarea element, 0 is returned.
+    BLINK_EXPORT int selectionStart() const;
+    // The returned value represents a cursor/caret position at the current
+    // selection's end for text input field or textarea. If neither input
+    // element nor textarea element, 0 is returned.
+    BLINK_EXPORT int selectionEnd() const;
+
     // Returns the name that should be used for the specified |element| when
     // storing autofill data.  This is either the field name or its id, an empty
     // string if it has no name and no id.
     BLINK_EXPORT WebString nameForAutofill() const;
 
     BLINK_EXPORT WebFormElement form() const;
 
 #if BLINK_IMPLEMENTATION
     WebFormControlElement(const WTF::PassRefPtr<WebCore::HTMLFormControlElement>&);
     WebFormControlElement& operator=(const WTF::PassRefPtr<WebCore::HTMLFormControlElement>&);
     operator WTF::PassRefPtr<WebCore::HTMLFormControlElement>() const;
 #endif
 };
 
 } // namespace blink
 
 #endif