Limit the number of history urls indexed for omnibox suggestions.

components/omnibox/browser/omnibox_field_trial.h

 // 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.
 
 #ifndef COMPONENTS_OMNIBOX_BROWSER_OMNIBOX_FIELD_TRIAL_H_
 #define COMPONENTS_OMNIBOX_BROWSER_OMNIBOX_FIELD_TRIAL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 388 matching lines @@
 
   // Returns the base relevance score for Physical Web omnibox suggestions when
   // the user has clicked on the omnibox but has not typed anything yet.
   static int GetPhysicalWebZeroSuggestBaseRelevance();
 
   // Returns the base relevance score for Physical Web omnibox suggestions when
   // the user has started typing in the omnibox.
   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.
 
   // Returns true whether the user is in the field trial which redirects zero
   // suggest requests to the service provided by the Chrome team.
   static bool InZeroSuggestRedirectToChromeFieldTrial();
 
   // Returns a string representing the address of the server where the zero
   // suggest requests are being redirected. The return value is a URL
   // (https://example.com/test) and it doesn't include any query component
@@ skipping 63 matching lines @@
   static const char kHUPNewScoringVisitedCountUseDecayFactorParam[];
 
   // Parameter names used by the HQP experimental scoring experiments.
   static const char kHQPExperimentalScoringBucketsParam[];
   static const char kHQPExperimentalScoringTopicalityThresholdParam[];
 
   // Parameter names used by the Physical Web experimental scoring experiments.
   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[];
   static const char kZeroSuggestRedirectToChromeAdditionalFieldsParam[];
 
   // The amount of time to wait before sending a new suggest request after the
   // previous one unless overridden by a field trial parameter.
   // Non-const because some unittests modify this value.
   static int kDefaultMinimumTimeBetweenSuggestQueriesMs;
 
@@ skipping 16 matching lines @@
   // prioritize different wildcard contexts, see the implementation.  How to
   // interpret the value is left to the caller; this is rule-dependent.
   static std::string GetValueForRuleInContext(
       const std::string& rule,
       metrics::OmniboxEventProto::PageClassification page_classification);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(OmniboxFieldTrial);
 };
 
 #endif  // COMPONENTS_OMNIBOX_BROWSER_OMNIBOX_FIELD_TRIAL_H_