Improvements to tab title prefix eliding as per email discussions.

chrome/browser/ui/title_prefix_matcher.h

 // Copyright (c) 2011 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_BROWSER_UI_TITLE_PREFIX_MATCHER_H_
 #define CHROME_BROWSER_UI_TITLE_PREFIX_MATCHER_H_
 #pragma once
 
 #include <vector>
 
 #include "base/string16.h"
+#include "googleurl/src/gurl.h"
 
 // This class exposes a static method that receives a vector of TitleInfo
 // objects so that it can find the length of the common prefixes among all
 // the titles. It can be used for tab titles for example so that the common
 // prefixes can be elided.
 // First, the caller needs to fill a vector of TitleInfo objects with the titles
 // for which they want to find the common prefix lengths. They can also provide
 // an optional caller_value where the index of the tabs could be saved
 // for example. This way the caller can remember which tab this title belongs
 // to, if not all tabs are passed into the vector.
 // When CalculatePrefixLengths returns, the TitleInfo objects in the vector
 // are set with the prefix_length that is common between this title
 // and at least one other.
 // Note that the prefix_length is only calculated at word boundaries.
 class TitlePrefixMatcher {
  public:
   struct TitleInfo {
-    TitleInfo(const string16* title, int caller_value);
+    TitleInfo(const string16* title, const GURL& url, int caller_value);
+    ~TitleInfo();
     // We assume the title string will be valid throughout the execution of
     // the prefix lengths calculation, and so we use a pointer to avoid an
     // unnecessary string copy.
     const string16* title;
+    // We only look for common prefix when the URL has the same hostname.
+    GURL url;
     // This contains the number of characters at the beginning of title that
     // are common with other titles in the TitleInfo vector.
     size_t prefix_length;
     // Utility data space for the caller. Unused by CalculatePrefixLengths.
     int caller_value;
   };
   static void CalculatePrefixLengths(std::vector<TitleInfo>* title_infos);
 
+  // We want to show the last few common chars of a page title in the tab,
+  // so we only do it if the common prefix is at least kMinElidingLength,
+  // otherwise, we could be replacing less characters than the ellipsis take.
+  static const int kCommonCharsToShow;
+  static const size_t kMinElidingLength;
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(TitlePrefixMatcher);
 };
 
 #endif  // CHROME_BROWSER_UI_TITLE_PREFIX_MATCHER_H_