Limit the number of history urls indexed for omnibox suggestions.

components/omnibox/browser/omnibox_field_trial.cc

 // Copyright 2014 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 "components/omnibox/browser/omnibox_field_trial.h"
 
 #include <cmath>
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 614 matching lines @@
       kPhysicalWebAfterTypingBaseRelevanceParam));
   int base_relevance;
   if (!param_value.empty() && base::StringToInt(param_value, &base_relevance))
     return base_relevance;
   // Default relevance score of the first Physical Web URL autocomplete match
   // when the user is typing in the omnibox.
   return 700;
 }
 
 // static
+int OmniboxFieldTrial::MaxNumHistoryUrlsIndexedAtStartup() {
+  std::string param_value(variations::GetVariationParamValue(
+      kBundledExperimentFieldTrialName,
+      kMaxNumHistoryUrlsIndexedAtStartupParam));
+  int num_urls;
+  if (!param_value.empty() && base::StringToInt(param_value, &num_urls))
+    return num_urls;
+  // Default value is set to -1 for unlimited number of urls.
+  return -1;
+}
+
+// static
 bool OmniboxFieldTrial::InZeroSuggestRedirectToChromeFieldTrial() {
   return base::FeatureList::IsEnabled(omnibox::kZeroSuggestRedirectToChrome);
 }
 
 // static
 std::string OmniboxFieldTrial::ZeroSuggestRedirectToChromeServerAddress() {
   return base::GetFieldTrialParamValueByFeature(
       omnibox::kZeroSuggestRedirectToChrome,
       kZeroSuggestRedirectToChromeServerAddressParam);
 }
@@ skipping 74 matching lines @@
     "HQPExperimentalScoringBuckets";
 const char
     OmniboxFieldTrial::kHQPExperimentalScoringTopicalityThresholdParam[] =
       "HQPExperimentalScoringTopicalityThreshold";
 
 const char OmniboxFieldTrial::kPhysicalWebZeroSuggestBaseRelevanceParam[] =
     "PhysicalWebZeroSuggestBaseRelevance";
 const char OmniboxFieldTrial::kPhysicalWebAfterTypingBaseRelevanceParam[] =
     "PhysicalWebAfterTypingBaseRelevanceParam";
 
+const char OmniboxFieldTrial::kMaxNumHistoryUrlsIndexedAtStartupParam[] =
+    "MaxNumHistoryUrlsIndexedAtStartup";
+
 const char OmniboxFieldTrial::kZeroSuggestRedirectToChromeServerAddressParam[] =
     "ZeroSuggestRedirectToChromeServerAddress";
 const char
     OmniboxFieldTrial::kZeroSuggestRedirectToChromeAdditionalFieldsParam[] =
         "ZeroSuggestRedirectToChromeAdditionalFields";
 
 // static
 int OmniboxFieldTrial::kDefaultMinimumTimeBetweenSuggestQueriesMs = 100;
 
 // Background and implementation details:
@@ skipping 51 matching lines @@
   if (it != params.end())
     return it->second;
   // Fall back to the global instant extended context.
   it = params.find(rule + ":" + page_classification_str + ":*");
   if (it != params.end())
     return it->second;
   // Look up rule in the global context.
   it = params.find(rule + ":*:*");
   return (it != params.end()) ? it->second : std::string();
 }