Limit the number of history urls indexed for omnibox suggestions.

components/omnibox/browser/omnibox_field_trial.cc

Index: components/omnibox/browser/omnibox_field_trial.cc
diff --git a/components/omnibox/browser/omnibox_field_trial.cc b/components/omnibox/browser/omnibox_field_trial.cc
index 378027ff0bc2748b7e25fac1086ed2b30034d053..11e23c127d5dc7814b8d12b5c271be4bacd734e0 100644
--- a/components/omnibox/browser/omnibox_field_trial.cc
+++ b/components/omnibox/browser/omnibox_field_trial.cc
@@ -632,6 +632,18 @@ int OmniboxFieldTrial::GetPhysicalWebAfterTypingBaseRelevance() {
 }
 
 // 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);
 }
@@ -726,6 +738,9 @@ const char OmniboxFieldTrial::kPhysicalWebZeroSuggestBaseRelevanceParam[] =
 const char OmniboxFieldTrial::kPhysicalWebAfterTypingBaseRelevanceParam[] =
     "PhysicalWebAfterTypingBaseRelevanceParam";
 
+const char OmniboxFieldTrial::kMaxNumHistoryUrlsIndexedAtStartupParam[] =
+    "MaxNumHistoryUrlsIndexedAtStartup";
+
 const char OmniboxFieldTrial::kZeroSuggestRedirectToChromeServerAddressParam[] =
     "ZeroSuggestRedirectToChromeServerAddress";
 const char