Delete backspace-for-back RuntimeFeature.

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

Index: third_party/WebKit/Source/core/editing/EditingBehavior.h
diff --git a/third_party/WebKit/Source/core/editing/EditingBehavior.h b/third_party/WebKit/Source/core/editing/EditingBehavior.h
index 5374bf1652af381a1efc0cdfc96b56b883b716a0..023555bcd3b56fd12c3319096deff07fa9854388 100644
--- a/third_party/WebKit/Source/core/editing/EditingBehavior.h
+++ b/third_party/WebKit/Source/core/editing/EditingBehavior.h
@@ -82,12 +82,6 @@ class CORE_EXPORT EditingBehavior {
     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