Create Field Trial param for whitelisting UKM Entries.

components/ukm/ukm_service.cc

Index: components/ukm/ukm_service.cc
diff --git a/components/ukm/ukm_service.cc b/components/ukm/ukm_service.cc
index a43f426f346986148a9a15738dfc4f7c2a885207..2d5272d552158d7821f8deedf7f3f3031c46724f 100644
--- a/components/ukm/ukm_service.cc
+++ b/components/ukm/ukm_service.cc
@@ -14,8 +14,10 @@
 #include "base/metrics/field_trial.h"
 #include "base/metrics/field_trial_params.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/metrics/metrics_hashes.h"
 #include "base/rand_util.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_split.h"
 #include "base/time/time.h"
 #include "components/metrics/metrics_log.h"
 #include "components/metrics/metrics_log_uploader.h"
@@ -68,6 +70,19 @@ std::string GetServerUrl() {
   return kDefaultServerUrl;
 }
 
+// Gets the list of whitelisted Entries as string.

[Alexei Svitkine (slow), 2017/03/14 15:40:56]

Is it comma-separated or something? Mention.

Or actually suggest doing the base::SplitString() here and returning the vector
- so the format of this param is localized to this function.

[rkaplow, 2017/03/14 18:01:41]

Done.

+std::string GetWhitelistEntries() {
+  return base::GetFieldTrialParamValueByFeature(kUkmFeature,
+                                                "WhitelistEntries");
+}
+
+// Returns true if we should use the whitelist of Entries to record.
+bool UseWhitelistEntries() {
+  // If the Field Trial param is empty, we will default to not using the
+  // whitelist.
+  return GetWhitelistEntries() != std::string();

[Alexei Svitkine (slow), 2017/03/14 15:40:56]

Nit: ! .empty()

[rkaplow, 2017/03/14 18:01:41]

Acknowledged.

+}
+
 // Gets the maximum number of Sources we'll keep in memory before discarding any
 // new ones being added.
 size_t GetMaxSources() {
@@ -126,6 +141,7 @@ enum class DroppedDataReason {
   NOT_DROPPED = 0,
   RECORDING_DISABLED = 1,
   MAX_HIT = 2,
+  NOT_WHITELISTED = 3,
   NUM_DROPPED_DATA_REASONS
 };
 
@@ -181,6 +197,8 @@ UkmService::UkmService(PrefService* pref_service,
 
   for (auto& provider : metrics_providers_)
     provider->Init();
+
+  StoreWhitelistedEntries();
 }
 
 UkmService::~UkmService() {
@@ -493,7 +511,22 @@ void UkmService::AddEntry(std::unique_ptr<UkmEntry> entry) {
     return;
   }
 
+  if (UseWhitelistEntries() &&

[Alexei Svitkine (slow), 2017/03/14 15:40:56]

Nit: I think it would be cleaner to just check
!whitelisted_entry_hashes_.empty() here and not use the extra helper.

[rkaplow, 2017/03/14 18:01:41]

agreed

+      !base::ContainsKey(whitelisted_entry_hashes_, entry->event_hash())) {
+    RecordDroppedEntry(DroppedDataReason::NOT_WHITELISTED);
+    return;
+  }
+
   entries_.push_back(std::move(entry));
 }
 
+void UkmService::StoreWhitelistedEntries() {
+  const auto entries =
+      base::SplitString(GetWhitelistEntries(), ",", base::TRIM_WHITESPACE,
+                        base::SPLIT_WANT_NONEMPTY);
+  for (const auto& entry_string : entries) {
+    whitelisted_entry_hashes_.insert(base::HashMetricName(entry_string));
+  }
+}
+
 }  // namespace ukm