Omnibox Metrics: Make |completed_length| field sane

chrome/browser/omnibox/omnibox_log.h

 // Copyright 2013 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_OMNIBOX_OMNIBOX_LOG_H_
 #define CHROME_BROWSER_OMNIBOX_OMNIBOX_LOG_H_
 
 #include <stddef.h>
 
 #include "base/strings/string16.h"
@@ skipping 55 matching lines @@
   // in the omnibox.  If at some point after modifying the text, the
   // user reverts the modifications (thus seeing the current web
   // page's URL again), then writes in the omnibox again, this time
   // delta should be computed starting from the second series of
   // modifications.  If we somehow skipped the logic to record
   // the time the user began typing (this should only happen in
   // unit tests), this elapsed time is set to -1 milliseconds.
   base::TimeDelta elapsed_time_since_user_first_modified_omnibox;
 
   // The number of extra characters the user would have to manually type
-  // if she/he were not given the opportunity to select this match.  Set to
-  // base::string16::npos if not available.
+  // if she/he were not given the opportunity to select this match.  Only
+  // set for matches that are allowed to be the default match (i.e., are
+  // inlineable).  Set to base::string16::npos if the match is not allowed
+  // to be the default match.
   size_t completed_length;
 
   // The amount of time since the last time the default (i.e., inline)
   // match changed.  This will certainly be less than
   // elapsed_time_since_user_first_modified_omnibox.  Measuring this
   // may be inappropriate in some cases (e.g., if editing is not in
   // progress).  In such cases, it's set to -1 milliseconds.
   base::TimeDelta elapsed_time_since_last_change_to_default_match;
 
   // Result set.
   const AutocompleteResult& result;
 
   // Diagnostic information from providers.  See
   // AutocompleteController::AddProvidersInfo() and
   // AutocompleteProvider::AddProviderInfo() above.
   ProvidersInfo providers_info;
 };
 
 #endif  // CHROME_BROWSER_OMNIBOX_OMNIBOX_LOG_H_