Add a NoStatePrefetch entry in about://flags

chrome/browser/about_flags.cc

 // Copyright (c) 2012 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 "chrome/browser/about_flags.h"
 
 #include <iterator>
 #include <map>
 #include <set>
 #include <utility>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/i18n/base_i18n_switches.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/metrics_hashes.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task_scheduler/switches.h"
 #include "base/values.h"
 #include "build/build_config.h"
 #include "cc/base/switches.h"
+#include "chrome/browser/prerender/prerender_field_trial.h"
 #include "chrome/common/channel_info.h"
 #include "chrome/common/chrome_content_client.h"
 #include "chrome/common/chrome_features.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/features.h"
 #include "chrome/grit/chromium_strings.h"
 #include "chrome/grit/generated_resources.h"
 #include "components/autofill/core/browser/autofill_experiments.h"
 #include "components/autofill/core/common/autofill_switches.h"
 #include "components/browser_sync/browser_sync_switches.h"
@@ skipping 593 matching lines @@
     {IDS_FLAGS_ENABLE_DEFAULT_MEDIA_SESSION_ENABLED,
      switches::kEnableDefaultMediaSession, ""},
 #if BUILDFLAG(ENABLE_PLUGINS)
     {IDS_FLAGS_ENABLE_DEFAULT_MEDIA_SESSION_ENABLED_DUCK_FLASH,
      switches::kEnableDefaultMediaSession,
      switches::kEnableDefaultMediaSessionDuckFlash},
 #endif  // BUILDFLAG(ENABLE_PLUGINS)
 };
 #endif  // !defined(OS_ANDROID)
 
+const FeatureEntry::FeatureParam kNoStatePrefetchEnabled[] = {
+    {prerender::kNoStatePrefetchFeatureModeParameterName,
+     prerender::kNoStatePrefetchFeatureModeParameterPrefetch}};
+
+const FeatureEntry::FeatureParam kNoStatePrefetchPrerender[] = {
+    {prerender::kNoStatePrefetchFeatureModeParameterName,
+     prerender::kNoStatePrefetchFeatureModeParameterPrerender}};
+
+const FeatureEntry::FeatureParam kNoStatePrefetchSimpleLoad[] = {
+    {prerender::kNoStatePrefetchFeatureModeParameterName,
+     prerender::kNoStatePrefetchFeatureModeParameterSimpleLoad}};
+
+const FeatureEntry::FeatureVariation kNoStatePrefetchFeatureVariations[] = {
+    {"No-state prefetch", kNoStatePrefetchEnabled,
+     arraysize(kNoStatePrefetchEnabled), nullptr},
+    {"Prerender", kNoStatePrefetchPrerender,
+     arraysize(kNoStatePrefetchPrerender), nullptr},
+    {"Simple load", kNoStatePrefetchSimpleLoad,
+     arraysize(kNoStatePrefetchSimpleLoad), nullptr}};
+
 // RECORDING USER METRICS FOR FLAGS:
 // -----------------------------------------------------------------------------
 // The first line of the entry is the internal name.
 //
 // To add a new entry, add to the end of kFeatureEntries. There are two
 // distinct types of entries:
 // . SINGLE_VALUE: entry is either on or off. Use the SINGLE_VALUE_TYPE
 //   macro for this type supplying the command line to the macro.
 // . MULTI_VALUE: a list of choices, the first of which should correspond to a
 //   deactivated state for this lab (i.e. no command line option).  To specify
@@ skipping 1453 matching lines @@
      IDS_FLAGS_CROSS_PROCESS_GUEST_VIEW_ISOLATION_DESCRIPTION, kOsDesktop,
      FEATURE_VALUE_TYPE(features::kGuestViewCrossProcessFrames)},
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
     {"media-remoting", IDS_FLAGS_MEDIA_REMOTING_NAME,
      IDS_FLAGS_MEDIA_REMOTING_DESCRIPTION, kOsDesktop,
      FEATURE_VALUE_TYPE(features::kMediaRemoting)},
     {"media-remoting-encrypted", IDS_FLAGS_MEDIA_REMOTING_ENCRYPTED_NAME,
      IDS_FLAGS_MEDIA_REMOTING_ENCRYPTED_DESCRIPTION, kOsDesktop,
      FEATURE_VALUE_TYPE(features::kMediaRemotingEncrypted)},
 #endif
+    {"enable-nostate-prefetch", IDS_FLAGS_NOSTATE_PREFETCH,
+     IDS_FLAGS_NOSTATE_PREFETCH_DESCRIPTION, kOsAll,
+     FEATURE_WITH_VARIATIONS_VALUE_TYPE(prerender::kNoStatePrefetchFeature,
+                                        kNoStatePrefetchFeatureVariations,
+                                        "NoStatePrefetchValidation")},
 
     // NOTE: Adding new command-line switches requires adding corresponding
     // entries to enum "LoginCustomFlags" in histograms.xml. See note in
     // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.

[droger, 2016/12/06 12:01:55]

Note: I am not sure if I have to do this or not, since I'm adding a feature and
not a switch.

Looking at other features, it seems inconsistent: some don't do it, other do it,
but use inconsistent values, i.e.:
* my-feature (which is the flag storage key for the feature)
* or my-feature:enabled
* or MyFeature (which is the feature name)

[droger, 2016/12/07 14:08:09]

+asvitkine: do you know what I should do here?

[droger, 2016/12/07 14:51:22]

I think I figured it out and updated histograms.xml, could you review the
changes there?

 };
 
 class FlagsStateSingleton {
  public:
   FlagsStateSingleton()
       : flags_state_(kFeatureEntries, arraysize(kFeatureEntries)) {}
   ~FlagsStateSingleton() {}
 
   static FlagsStateSingleton* GetInstance() {
     return base::Singleton<FlagsStateSingleton>::get();
@@ skipping 185 matching lines @@
 const base::HistogramBase::Sample kBadSwitchFormatHistogramId = 0;
 
 const FeatureEntry* GetFeatureEntries(size_t* count) {
   *count = arraysize(kFeatureEntries);
   return kFeatureEntries;
 }
 
 }  // namespace testing
 
 }  // namespace about_flags