Delete backspace-for-back RuntimeFeature.

third_party/WebKit/Source/core/editing/EditingBehavior.h

 /*
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 64 matching lines @@
   bool ShouldAlwaysGrowSelectionWhenExtendingToBoundary() const {
     return type_ == kEditingMacBehavior;
   }
 
   // On Mac, when processing a contextual click, the object being clicked upon
   // should be selected.
   bool ShouldSelectOnContextualMenuClick() const {
     return type_ == kEditingMacBehavior;
   }
 
-  // On Mac and Windows, pressing backspace (when it isn't handled otherwise)
-  // should navigate back.
-  bool ShouldNavigateBackOnBackspace() const {
-    return type_ != kEditingUnixBehavior && type_ != kEditingAndroidBehavior;
-  }
-
   // On Mac, selecting backwards by word/line from the middle of a word/line,
   // and then going forward leaves the caret back in the middle with no
   // selection, instead of directly selecting to the other end of the line/word
   // (Unix/Windows behavior).
   bool ShouldExtendSelectionByWordOrLineAcrossCaret() const {
     return type_ != kEditingMacBehavior;
   }
 
   // Based on native behavior, when using ctrl(alt)+arrow to move caret by word,
   // ctrl(alt)+left arrow moves caret to immediately before the word in all
@@ skipping 24 matching lines @@
 
   bool ShouldInsertCharacter(const KeyboardEvent&) const;
 
  private:
   EditingBehaviorType type_;
 };
 
 }  // namespace blink
 
 #endif  // EditingBehavior_h