[Cleanup] Clean up the VariationsFieldTrialCreator code.

* Dramatically simplifies the test code, plus tests the public API rather than
  an internal API method.
* Declares said internal API method with private visibility.
* Updates a non-const reference returned type to be a pointer instead.
* Tucks an enum into the anonymous namespace in the implementation file.
* Fixes up some comments: clearer phrasing, plus fixed typos and wrapping.

R=holte@chromium.org

Bug: 727984
Change-Id: I4c394d04cb4f4d24cdcc8a7baa2db54f4dc5c8f7
Reviewed-on: https://chromium-review.googlesource.com/826493Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524276}

components/variations/service/variations_field_trial_creator.cc

@@ -42,6 +42,23 @@ enum VariationsSeedExpiry {
   VARIATIONS_SEED_EXPIRY_ENUM_SIZE,
 };
 
+// Set of different possible values to report for the
+// Variations.LoadPermanentConsistencyCountryResult histogram. Values are
+// persisted to logs, and should therefore never be renumbered nor reused.
+enum LoadPermanentConsistencyCountryResult {
+  LOAD_COUNTRY_NO_PREF_NO_SEED = 0,
+  LOAD_COUNTRY_NO_PREF_HAS_SEED,
+  LOAD_COUNTRY_INVALID_PREF_NO_SEED,
+  LOAD_COUNTRY_INVALID_PREF_HAS_SEED,
+  LOAD_COUNTRY_HAS_PREF_NO_SEED_VERSION_EQ,
+  LOAD_COUNTRY_HAS_PREF_NO_SEED_VERSION_NEQ,
+  LOAD_COUNTRY_HAS_BOTH_VERSION_EQ_COUNTRY_EQ,
+  LOAD_COUNTRY_HAS_BOTH_VERSION_EQ_COUNTRY_NEQ,
+  LOAD_COUNTRY_HAS_BOTH_VERSION_NEQ_COUNTRY_EQ,
+  LOAD_COUNTRY_HAS_BOTH_VERSION_NEQ_COUNTRY_NEQ,
+  LOAD_COUNTRY_MAX,
+};
+
 // Gets current form factor and converts it from enum DeviceFormFactor to enum
 // Study_FormFactor.
 Study::FormFactor GetCurrentFormFactor() {

components/variations/service/variations_field_trial_creator.h

@@ -33,18 +33,7 @@ class VariationsFieldTrialCreator {
   // empty if it is not available.
   std::string GetLatestCountry() const;
 
-  // Creates field trials based on the variations seed loaded from local state.
-  // If there is a problem loading the seed data, all trials specified by the
-  // seed may not be created. Some field trials are configured to override or
-  // associate with (for reporting) specific features. These associations are
-  // registered with |feature_list|.
-  bool CreateTrialsFromSeed(
-      std::unique_ptr<const base::FieldTrial::EntropyProvider>
-          low_entropy_provider,
-      base::FeatureList* feature_list);
-
-  VariationsSeedStore& seed_store() { return seed_store_; }
-
+  VariationsSeedStore* seed_store() { return &seed_store_; }
   const VariationsSeedStore& seed_store() const { return seed_store_; }
 
   bool create_trials_from_seed_called() const {
@@ -96,36 +85,27 @@ class VariationsFieldTrialCreator {
   // Records the time of the most recent successful fetch.
   void RecordLastFetchTime();
 
-  // Loads the seed from the variations store into |seed|. If successfull,
-  // |seed| will contain the loaded data and true is returned. Set as virtual
-  // so that it can be overridden by tests.
+  // Loads the seed from the variations store into |seed|. If successful, |seed|
+  // will contain the loaded data and true is returned. Virtual for testing.
   virtual bool LoadSeed(VariationsSeed* seed);
 
-  // Allow the platform that is used to filter the set of active trials
-  // to be overridden.
+  // Allow the platform that is used to filter the set of active trials to be
+  // overridden.
   void OverrideVariationsPlatform(Study::Platform platform_override);
 
  private:
   PrefService* local_state() { return seed_store_.local_state(); }
-
   const PrefService* local_state() const { return seed_store_.local_state(); }
 
-  // Set of different possible values to report for the
-  // Variations.LoadPermanentConsistencyCountryResult histogram. This enum must
-  // be kept consistent with its counterpart in histograms.xml.
-  enum LoadPermanentConsistencyCountryResult {
-    LOAD_COUNTRY_NO_PREF_NO_SEED = 0,
-    LOAD_COUNTRY_NO_PREF_HAS_SEED,
-    LOAD_COUNTRY_INVALID_PREF_NO_SEED,
-    LOAD_COUNTRY_INVALID_PREF_HAS_SEED,
-    LOAD_COUNTRY_HAS_PREF_NO_SEED_VERSION_EQ,
-    LOAD_COUNTRY_HAS_PREF_NO_SEED_VERSION_NEQ,
-    LOAD_COUNTRY_HAS_BOTH_VERSION_EQ_COUNTRY_EQ,
-    LOAD_COUNTRY_HAS_BOTH_VERSION_EQ_COUNTRY_NEQ,
-    LOAD_COUNTRY_HAS_BOTH_VERSION_NEQ_COUNTRY_EQ,
-    LOAD_COUNTRY_HAS_BOTH_VERSION_NEQ_COUNTRY_NEQ,
-    LOAD_COUNTRY_MAX,
-  };
+  // Creates field trials based on the variations seed loaded from local state.
+  // If there is a problem loading the seed data, all trials specified by the
+  // seed may not be created. Some field trials are configured to override or
+  // associate with (for reporting) specific features. These associations are
+  // registered with |feature_list|.
+  bool CreateTrialsFromSeed(
+      std::unique_ptr<const base::FieldTrial::EntropyProvider>
+          low_entropy_provider,
+      base::FeatureList* feature_list);
 
   VariationsServiceClient* client_;
 

components/variations/service/variations_service.cc

@@ -436,7 +436,7 @@ bool VariationsService::StoreSeed(const std::string& seed_data,
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
   std::unique_ptr<VariationsSeed> seed(new VariationsSeed);
-  if (!field_trial_creator_.seed_store().StoreSeedData(
+  if (!field_trial_creator_.seed_store()->StoreSeedData(
           seed_data, seed_signature, country_code, date_fetched,
           is_delta_compressed, is_gzip_compressed, seed.get())) {
     return false;
@@ -499,14 +499,14 @@ bool VariationsService::DoFetchFromURL(const GURL& url) {
                                       net::LOAD_DO_NOT_SAVE_COOKIES);
   pending_seed_request_->SetRequestContext(client_->GetURLRequestContext());
   bool enable_deltas = false;
-  if (!field_trial_creator_.seed_store().variations_serial_number().empty() &&
+  if (!field_trial_creator_.seed_store()->variations_serial_number().empty() &&
       !disable_deltas_for_next_request_) {
     // Tell the server that delta-compressed seeds are supported.
     enable_deltas = true;
     // Get the seed only if its serial number doesn't match what we have.
     // If the fetch is being done over HTTP, encrypt the If-None-Match header.
     const std::string& original_sn =
-        field_trial_creator_.seed_store().variations_serial_number();
+        field_trial_creator_.seed_store()->variations_serial_number();
     if (!url.SchemeIs(url::kHttpsScheme) &&
         base::FeatureList::IsEnabled(kHttpRetryFeature)) {
       std::string encrypted_sn;
@@ -666,7 +666,7 @@ void VariationsService::OnURLFetchComplete(const net::URLFetcher* source) {
 
       // Update the seed date value in local state (used for expiry check on
       // next start up), since 304 is a successful response.
-      field_trial_creator_.seed_store().UpdateSeedDateAndLogDayChange(
+      field_trial_creator_.seed_store()->UpdateSeedDateAndLogDayChange(
           response_date);
     }
     return;
@@ -683,7 +683,7 @@ void VariationsService::OnURLFetchComplete(const net::URLFetcher* source) {
                                 &is_gzip_compressed)) {
     // The header does not specify supported instance manipulations, unable to
     // process data. Details of errors were logged by GetInstanceManipulations.
-    field_trial_creator_.seed_store().ReportUnsupportedSeedFormatError();
+    field_trial_creator_.seed_store()->ReportUnsupportedSeedFormatError();
     return;
   }