Making VisibleSelection operator== take base and extent into account.

Source/core/editing/VisibleSelection.h

 /*
  * Copyright (C) 2004 Apple Computer, 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 164 matching lines @@
     RawPtrWillBeMember<ChangeObserver> m_changeObserver;
 
     // these are cached, can be recalculated by validate()
     SelectionType m_selectionType; // None, Caret, Range
     bool m_baseIsFirst : 1; // True if base is before the extent
     bool m_isDirectional : 1; // Non-directional ignores m_baseIsFirst and selection always extends on shift + arrow key.
 };
 
 inline bool operator==(const VisibleSelection& a, const VisibleSelection& b)
 {
     return a.start() == b.start() && a.end() == b.end() && a.affinity() == b.affinity() && a.isBaseFirst() == b.isBaseFirst()

[yosin_UTC9, 2015/04/16 04:59:04]

if one of selections is null, we don't need to check start/end and base/extent.
So, we could write:

if (a.affinity() != b.affinity() || a.isDirectional() != b.isDirectional())
  return false;

if (a.isNull())
  return b.isNull();

return a.start() == b.start() && a.end() == b.end() && a.base() == b.base() &&
a.extent() == b.extent();

[yosin_UTC9, 2015/04/16 04:59:04]

Since we compare base/extent equality, we don't need to check equality of
|isBaseFirst()|.

[mfomitchev, 2015/04/16 18:11:32]

Added the None check and removed isBaseFirst() check. Other than that, I am not
sure we need to explicitly short-circuit: if any of the == evaluate to false, it
won't evaluate any other == anyway. And it seems that checking start/end
positions first is pretty effective in eliminating unequal results right away.
Even if this makes sense, I don't think it needs to be a part of this CL.

-        && a.isDirectional() == b.isDirectional();
+        && a.isDirectional() == b.isDirectional() && a.base() == b.base() && a.extent() == b.extent();
 }
 
 inline bool operator!=(const VisibleSelection& a, const VisibleSelection& b)
 {
     return !(a == b);
 }
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showTree(const blink::VisibleSelection&);
 void showTree(const blink::VisibleSelection*);
 #endif
 
 #endif // VisibleSelection_h