Limit the number of history urls indexed for omnibox suggestions.

components/omnibox/browser/omnibox_field_trial.h

Index: components/omnibox/browser/omnibox_field_trial.h
diff --git a/components/omnibox/browser/omnibox_field_trial.h b/components/omnibox/browser/omnibox_field_trial.h
index 82185aaf3dec36da126ca7e3e804061fabc24a43..d17938e0dcee8130476ca2661ff7a60f143dd5b5 100644
--- a/components/omnibox/browser/omnibox_field_trial.h
+++ b/components/omnibox/browser/omnibox_field_trial.h
@@ -406,6 +406,15 @@ class OmniboxFieldTrial {
   static int GetPhysicalWebAfterTypingBaseRelevance();
 
   // ---------------------------------------------------------
+  // For experitment to limit url indexing that's part of the bundled omnibox
+  // field trial.
+
+  // Returns the maximum number of history urls to index at the startup. Note:

[Mark P, 2017/05/08 22:39:17]

There are multiple history systems.  You're only limiting one.  This comment and
function name should mention which one you're talking about here (HistoryQuick
provider).  You can use HQP in the function name, enough people who touch this
file will recognize that.

ditto const below

[ssid, 2017/05/10 01:01:35]

Ah sorry. I coulnd't find what hqp means from the code. So, I just named it
history after your last comment.
Fixed thanks!

[Mark P, 2017/05/10 17:23:09]

Yeah, I agree the names are confusing.

The basic structure is that the "URL Index Private Data" is an index used by
"History Quick Provider", the omnibox system that's supposed to search most of
the user's history intelligently and quickly.

[ssid, 2017/05/10 19:47:57]

Acknowledged.

+  // this limit is only applied at startup and more urls can be indexed during
+  // the session. Returns -1 if limit is not set by trials.
+  static int MaxNumHistoryUrlsIndexedAtStartup();
+
+  // ---------------------------------------------------------
   // For experiment redirecting zero suggest requests to a service provided by
   // the Chrome team.
 
@@ -489,6 +498,10 @@ class OmniboxFieldTrial {
   static const char kPhysicalWebZeroSuggestBaseRelevanceParam[];
   static const char kPhysicalWebAfterTypingBaseRelevanceParam[];
 
+  // Parameter name used by the experiment that limits the number of history
+  // urls indexed for suggestions.
+  static const char kMaxNumHistoryUrlsIndexedAtStartupParam[];
+
   // Parameter names used by the experiment redirecting Zero Suggestion requests
   // to a service provided by the Chrome team.
   static const char kZeroSuggestRedirectToChromeServerAddressParam[];