Add Feature params for UKM Service to control thresholds on sources and 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 87176c714a5f3e4938b80cd0ec71ede2eeb7ca47..e325ddca93bbf650260750543d8dcb304adb1c44 100644
--- a/components/ukm/ukm_service.cc
+++ b/components/ukm/ukm_service.cc
@@ -63,11 +63,11 @@ constexpr size_t kMaxLogRetransmitSize = 100 * 1024;
 
 // Maximum number of Sources we'll keep in memory before discarding any
 // new ones being added.
-const size_t kMaxSources = 500;
+const size_t kDefaultMaxSources = 500;
 
 // Maximum number of Entries we'll keep in memory before discarding any
 // new ones being added.
-const size_t kMaxEntries = 5000;
+const size_t kDefaultMaxEntries = 5000;
 
 std::string GetServerUrl() {
   std::string server_url =
@@ -77,6 +77,16 @@ std::string GetServerUrl() {
   return kDefaultServerUrl;
 }
 
+size_t GetMaxSources() {

[Alexei Svitkine (slow), 2017/03/02 23:13:42]

Nit: Can you add comments to these?

+  return static_cast<size_t>(base::GetFieldTrialParamByFeatureAsInt(
+      kUkmFeature, "MaxSources", kDefaultMaxSources));
+}
+
+size_t GetMaxEntries() {
+  return static_cast<size_t>(base::GetFieldTrialParamByFeatureAsInt(
+      kUkmFeature, "MaxEntries", kDefaultMaxEntries));
+}
+
 bool ShouldRecordInitialUrl() {
   return base::GetFieldTrialParamByFeatureAsBool(kUkmFeature,
                                                  "RecordInitialUrl", false);
@@ -418,7 +428,7 @@ void UkmService::RecordSource(std::unique_ptr<UkmSource> source) {
     RecordDroppedSource(DroppedDataReason::RECORDING_DISABLED);
     return;
   }
-  if (sources_.size() >= kMaxSources) {
+  if (sources_.size() >= GetMaxSources()) {
     RecordDroppedSource(DroppedDataReason::MAX_HIT);
     return;
   }
@@ -459,7 +469,7 @@ void UkmService::UpdateSourceURL(int32_t source_id, const GURL& url) {
     return;
   }
 
-  if (sources_.size() >= kMaxSources) {
+  if (sources_.size() >= GetMaxSources()) {
     RecordDroppedSource(DroppedDataReason::MAX_HIT);
     return;
   }
@@ -476,7 +486,7 @@ void UkmService::AddEntry(std::unique_ptr<UkmEntry> entry) {
     RecordDroppedEntry(DroppedDataReason::RECORDING_DISABLED);
     return;
   }
-  if (entries_.size() >= kMaxEntries) {
+  if (entries_.size() >= GetMaxEntries()) {
     RecordDroppedEntry(DroppedDataReason::MAX_HIT);
     return;
   }