[Autofill/Autocomplete Feature] Substring matching instead of prefix matching (Blink).

Source/core/html/HTMLTextFormControlElement.h

Index: Source/core/html/HTMLTextFormControlElement.h
diff --git a/Source/core/html/HTMLTextFormControlElement.h b/Source/core/html/HTMLTextFormControlElement.h
index 95a131ba743bec1388816d5baa6c1f9f98f3ca42..68b93eb4aaa3494a8fe0cbeb9cfb600aa26c8397 100644
--- a/Source/core/html/HTMLTextFormControlElement.h
+++ b/Source/core/html/HTMLTextFormControlElement.h
@@ -80,6 +80,8 @@ public:
     void setSelectionRange(int start, int end, const String& direction);
     void setSelectionRange(int start, int end, TextFieldSelectionDirection = SelectionHasNoDirection, NeedToDispatchSelectEvent = DispatchSelectEvent, SelectionOption = ChangeSelection);
     PassRefPtrWillBeRawPtr<Range> selection() const;
+    void setSuggestedValueStart(int start) { m_suggestedValueStartOffset = start; }
+    int suggestedValueStart() const { return m_suggestedValueStartOffset; }
 
     virtual bool supportsAutocapitalize() const = 0;
     virtual const AtomicString& defaultAutocapitalize() const = 0;
@@ -157,6 +159,7 @@ private:
     String m_textAsOfLastFormControlChangeEvent;
     bool m_lastChangeWasUserEdit;
 
+    int m_suggestedValueStartOffset;
     int m_cachedSelectionStart;
     int m_cachedSelectionEnd;
     TextFieldSelectionDirection m_cachedSelectionDirection;