Limit the number of history urls indexed for omnibox suggestions.

components/omnibox/browser/url_index_private_data.cc

Index: components/omnibox/browser/url_index_private_data.cc
diff --git a/components/omnibox/browser/url_index_private_data.cc b/components/omnibox/browser/url_index_private_data.cc
index b9f2a93ea945bc2e73e33afdb396d0bd0ef8a975..d59c2f9339e6d429ad4c71cc09e1a3f68a0935f5 100644
--- a/components/omnibox/browser/url_index_private_data.cc
+++ b/components/omnibox/browser/url_index_private_data.cc
@@ -397,8 +397,24 @@ scoped_refptr<URLIndexPrivateData> URLIndexPrivateData::RebuildFromHistory(
   history::URLDatabase::URLEnumerator history_enum;
   if (!history_db->InitURLEnumeratorForSignificant(&history_enum))
     return nullptr;
+
   rebuilt_data->last_time_rebuilt_from_history_ = base::Time::Now();
+
+  // Limit the nuber of URLs indexed on low end devices. This would degrade the

[Mark P, 2017/05/07 21:32:38]

nit: would degrade -> degrades

+  // quality of suggestions to save memory.
+  int max_history_urls_indexed = -1;  // unlimited
+  if (base::SysInfo::IsLowEndDevice()) {
+    std::string limit =
+        base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+            switches::kLimitHistoryUrlIndexingForOmnibox);
+    if (!limit.empty() && !base::StringToInt(limit, &max_history_urls_indexed))
+      max_history_urls_indexed = -1;
+  }
+
+  int num_urls_indexed = 0;
   for (history::URLRow row; history_enum.GetNextURL(&row);) {
+    if (++num_urls_indexed == max_history_urls_indexed)
+      break;
     rebuilt_data->IndexRow(
         history_db, nullptr, row, scheme_whitelist, nullptr);
   }