Modified GetMatchToPrefetch() to return a valid match for prefetching even when hide_verbatim flag i

chrome/browser/ui/omnibox/omnibox_controller.cc

 // 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.
 
 #include "chrome/browser/ui/omnibox/omnibox_controller.h"
 
 #include "base/metrics/histogram.h"
 #include "chrome/browser/autocomplete/autocomplete_classifier.h"
 #include "chrome/browser/autocomplete/autocomplete_match.h"
 #include "chrome/browser/autocomplete/search_provider.h"
@@ skipping 13 matching lines @@
 #include "extensions/common/constants.h"
 #include "ui/gfx/rect.h"
 
 namespace {
 
 // Returns the AutocompleteMatch that the InstantController should prefetch, if
 // any.
 //
 // The SearchProvider may mark some suggestions to be prefetched based on
 // instructions from the suggest server. If such a match ranks sufficiently
-// highly, we'll return it. We only care about matches that are the default or
-// else the very first entry in the dropdown (which can happen for non-default
-// matches only if we're hiding a top verbatim match); for other matches, we
-// think the likelihood of the user selecting them is low enough that
-// prefetching isn't worth doing.
+// highly, we'll return it. We only care about matches that are the default; for
+// other matches, we think the likelihood of the user selecting them is low
+// enough that prefetching isn't worth doing.
 const AutocompleteMatch* GetMatchToPrefetch(const AutocompleteResult& result) {
   const AutocompleteResult::const_iterator default_match(
       result.default_match());
-  if (default_match == result.end())
-    return NULL;
-
-  if (SearchProvider::ShouldPrefetch(*default_match))
-    return &(*default_match);
-
-  return (result.ShouldHideTopMatch() && (result.size() > 1) &&
-      SearchProvider::ShouldPrefetch(result.match_at(1))) ?
-          &result.match_at(1) : NULL;
+  return ((default_match != result.end()) &&

[samarth, 2013/11/14 16:17:45]

This isn't quite right.  Let's say we have the following state:
 
  faceb|
+------------+
  faceb
  facebook (p)
  ...

The user has typed [faceb].  The top match is the verbatim match.  But the top
match returned by the server is [facebook] and has been marked for prefetch.

If hide-verbatim was on, the [faceb] verbatim match would have been hidden and
your old logic would kick off prefetching for [facebook].  Great!

Unfortunately, it seems like hide-verbatim is not going to work without the
addition of some UI element that lets user click to search (many users dont hit
enter).  Until such time, we really still should prefetch [facebook] at this
point.  Otherwise, we'd require the user to fully type out [facebook] before we
ever prefetch it, which would kill most of the speed benefits of this feature.

So what I'd suggest is keeping your old logic here but making a version of
ShouldHideTopMatch that doesn't check the field trial bit (perhaps
CanHideTopMatch or TopMatchIsVerbatim -- Peter probably will have a good
suggestion here) and use that.

+Peter: sound OK to you?

[kmadhusu, 2013/12/12 01:04:01]

Fixed. Added a new function in AutocompleteResult.

+      SearchProvider::ShouldPrefetch(*default_match)) ? &(*default_match) :
+          NULL;
 }
 
 }  // namespace
 
 OmniboxController::OmniboxController(OmniboxEditModel* omnibox_edit_model,
                                      Profile* profile)
     : omnibox_edit_model_(omnibox_edit_model),
       profile_(profile),
       autocomplete_controller_(new AutocompleteController(profile, this,
           AutocompleteClassifier::kDefaultOmniboxProviders)) {
@@ skipping 85 matching lines @@
     if (profile_->GetNetworkPredictor()) {
       profile_->GetNetworkPredictor()->AnticipateOmniboxUrl(
           match.destination_url,
           predictors::AutocompleteActionPredictor::IsPreconnectable(match));
     }
     // We could prefetch the alternate nav URL, if any, but because there
     // can be many of these as a user types an initial series of characters,
     // the OS DNS cache could suffer eviction problems for minimal gain.
   }
 }