Only send SelectionChanged events when the selection has actually changed....

chrome/renderer/render_view.h

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_RENDERER_RENDER_VIEW_H_
 #define CHROME_RENDERER_RENDER_VIEW_H_
 
 #include <string>
 #include <queue>
 #include <vector>
@@ skipping 780 matching lines @@
   // it's for the selection clipboard.
   std::string selection_text_;
 
   // Cache the preferred width of the page in order to prevent sending the IPC
   // when layout() recomputes it but it doesn't actually change.
   int preferred_width_;
 
   // If true, we send IPC messages when the preferred width changes.
   bool send_preferred_width_changes_;
 
+  // The text selection the last time DidChangeSelection got called.
+  std::string last_selection_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderView);
 };
 
 #endif  // CHROME_RENDERER_RENDER_VIEW_H_