Add fallback to MostVisited URLs when pers 0-query is not supported.

This CL adds a fallback to display MostVisited URLs when personalized
zero-query is enabled with ChromeHomePersonalizedOmniboxSuggestions but
the user's default search engine is not Google.

Bug: 781994
Change-Id: I489052f3a33e2f97d86138760f8f2d135515c241
Reviewed-on: https://chromium-review.googlesource.com/777502
Commit-Queue: Gheorghe Comanici <gcomanici@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519855}

components/omnibox/browser/omnibox_field_trial.cc

@@ -333,6 +333,7 @@ bool OmniboxFieldTrial::InZeroSuggestMostVisitedWithoutSerpFieldTrial(
 #endif
 }
 
+// static
 bool OmniboxFieldTrial::InZeroSuggestPersonalizedFieldTrial(
     PrefService* prefs) {
   std::string variant(variations::GetVariationParamValue(

components/omnibox/browser/zero_suggest_provider.cc

@@ -35,6 +35,7 @@
 #include "components/omnibox/browser/verbatim_match.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/prefs/pref_service.h"
+#include "components/search_engines/search_engine_type.h"
 #include "components/search_engines/template_url_service.h"
 #include "components/url_formatter/url_formatter.h"
 #include "components/variations/net/variations_http_headers.h"
@@ -86,6 +87,31 @@ const int kDefaultZeroSuggestRelevance = 100;
 // Used for testing whether zero suggest is ever available.
 constexpr char kArbitraryInsecureUrlString[] = "http://www.google.com/";
 
+// Used to determine whether or not Most Visited URLs will be displayed.
+// This is true in either of these two cases:
+//   1. The user is in zero suggest most visited field trial.
+//   2. The user is in zero suggest field trial that enables search-for
+//      queries as suggestions and the user does not have Google set up as
+//      their default search engine
+bool DisplayZeroSuggestMostVisitedURLs(
+    PrefService* prefs,
+    const TemplateURLService* template_url_service) {
+  if (OmniboxFieldTrial::InZeroSuggestMostVisitedFieldTrial(prefs))
+    return true;
+
+  if (OmniboxFieldTrial::InZeroSuggestPersonalizedFieldTrial(prefs) &&
+      template_url_service != nullptr) {
+    const TemplateURL* default_provider =
+        template_url_service->GetDefaultSearchProvider();
+    return default_provider == nullptr ||
+           default_provider->GetEngineType(
+               template_url_service->search_terms_data()) !=
+               SEARCH_ENGINE_GOOGLE;
+  }
+
+  return false;
+}
+
 }  // namespace
 
 // static
@@ -170,8 +196,8 @@ void ZeroSuggestProvider::Start(const AutocompleteInput& input,
   // suggestions, if based on local browsing history.
   MaybeUseCachedSuggestions();
 
-  if (OmniboxFieldTrial::InZeroSuggestMostVisitedFieldTrial(
-          client()->GetPrefs())) {
+  if (DisplayZeroSuggestMostVisitedURLs(client()->GetPrefs(),
+                                        template_url_service)) {
     most_visited_urls_.clear();
     scoped_refptr<history::TopSites> ts = client()->GetTopSites();
     if (ts) {
@@ -442,8 +468,8 @@ void ZeroSuggestProvider::ConvertResultsToAutocompleteMatches() {
   UMA_HISTOGRAM_COUNTS("ZeroSuggest.AllResults", num_results);
 
   // Show Most Visited results after ZeroSuggest response is received.
-  if (OmniboxFieldTrial::InZeroSuggestMostVisitedFieldTrial(
-          client()->GetPrefs())) {
+  if (DisplayZeroSuggestMostVisitedURLs(client()->GetPrefs(),
+                                        template_url_service)) {
     if (!current_url_match_.destination_url.is_valid())
       return;
     matches_.push_back(current_url_match_);