Allow non default prefetch suggestions to be prefetched

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 12 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.
+// highly or if allow_prefetch_non_default_match field trial is enabled, we'll
+// return it.
 //
-// We only care about matches that are the default or the very first entry in
-// the dropdown (which can happen for non-default matches only if we're hiding
-// a top verbatim match) or the second entry in the dropdown (which can happen
-// for non-default matches when a top verbatim match is shown); for other
-// matches, we think the likelihood of the user selecting them is low enough
-// that prefetching isn't worth doing.
+// If the allow_prefetch_non_default_match field trial is enabled we return the

[kmadhusu, 2014/06/18 17:07:38]

s/allow_prefetch_.../kAllowPrefetchNonDefaultMatch/g

[sidharthms, 2014/06/18 22:45:22]

Done.

+// prefetch suggestion even if it is not the default match. Otherwise we only
+// care about matches that are the default or the very first entry in the
+// dropdown (which can happen for non-default matches only if we're hiding a top
+// verbatim match) or the second entry in the dropdown (which can happen for
+// non-default matches when a top verbatim match is shown); 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) {
-  // If the default match should be prefetched, do that.
-  const AutocompleteResult::const_iterator default_match(
-      result.default_match());
-  if ((default_match != result.end()) &&
-      SearchProvider::ShouldPrefetch(*default_match))
-    return &(*default_match);
+  if (chrome::ShouldAllowPrefetchNonDefaultMatch()) {
+    const AutocompleteResult::const_iterator prefetch_match = std::find_if(
+        result.begin(), result.end(), SearchProvider::ShouldPrefetch);
+    if (prefetch_match != result.end())

[kmadhusu, 2014/06/18 17:07:38]

nit: You can use a ternary operator here and remove the else block. 

return prefetch_match != result.end() ? &(*prefetch_match) : NULL;

[sidharthms, 2014/06/18 22:45:22]

Done.

+      return &(*prefetch_match);

[kmadhusu, 2014/06/18 17:07:38]

As you said yesterday, when we type "ya" we are submitting a prefetch request
for the search query "youtube". We should figure out why that's happening. (FYI)
When we sent a request to fetch results for "youtube", "youtube" was not
displayed in the suggestions list. 

[sidharthms, 2014/06/18 22:45:22]

Done.

+  } else {
+    // If the default match should be prefetched, do that.
+    const AutocompleteResult::const_iterator default_match(
+        result.default_match());
+    if ((default_match != result.end()) &&
+        SearchProvider::ShouldPrefetch(*default_match))
+      return &(*default_match);
 
-  // Otherwise, if the top match is a verbatim match and the very next match is
-  // prefetchable, fetch that.
-  if ((result.ShouldHideTopMatch() ||
-       result.TopMatchIsStandaloneVerbatimMatch()) &&
-      (result.size() > 1) &&
-      SearchProvider::ShouldPrefetch(result.match_at(1)))
-    return &result.match_at(1);
-
+    // Otherwise, if the top match is a verbatim match and the very next match
+    // is prefetchable, fetch that.
+    if ((result.ShouldHideTopMatch() ||
+         result.TopMatchIsStandaloneVerbatimMatch()) &&
+        (result.size() > 1) &&
+        SearchProvider::ShouldPrefetch(result.match_at(1)))
+      return &result.match_at(1);
+  }
   return NULL;
 }
 
 }  // namespace
 
 OmniboxController::OmniboxController(OmniboxEditModel* omnibox_edit_model,
                                      Profile* profile)
     : omnibox_edit_model_(omnibox_edit_model),
       profile_(profile),
       popup_(NULL),
@@ skipping 75 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.
   }
 }