MediaCapabilities: make DB configurable via Finch.

Adds flags for configuring the size of the rolling window and the number
of days to keep stats before expiring.

Bug: 910404
Test: new unit tests
Change-Id: I8a88a81154c710a1cc9b029e2b8ef8af61d945e0
Reviewed-on: https://chromium-review.googlesource.com/c/1355996Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612479}

media/capabilities/video_decode_stats_db_impl.cc

@@ -10,11 +10,13 @@
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/field_trial_params.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/sequence_checker.h"
 #include "base/task/post_task.h"
 #include "base/time/default_clock.h"
 #include "components/leveldb_proto/proto_database_impl.h"
+#include "media/base/media_switches.h"
 #include "media/capabilities/video_decode_stats.pb.h"
 
 namespace media {
@@ -27,8 +29,32 @@ namespace {
 // See comments in components/leveldb_proto/leveldb_database.h
 const char kDatabaseClientName[] = "VideoDecodeStatsDB";
 
+const int kMaxFramesPerBufferDefault = 2500;
+
+const int kMaxDaysToKeepStatsDefault = 30;
+
 };  // namespace
 
+const char VideoDecodeStatsDBImpl::kMaxFramesPerBufferParamName[] =
+    "db_frames_buffer_size";
+
+const char VideoDecodeStatsDBImpl::kMaxDaysToKeepStatsParamName[] =
+    "db_days_to_keep_stats";
+
+// static
+int VideoDecodeStatsDBImpl::GetMaxFramesPerBuffer() {
+  return base::GetFieldTrialParamByFeatureAsDouble(
+      kMediaCapabilitiesWithParameters, kMaxFramesPerBufferParamName,
+      kMaxFramesPerBufferDefault);
+}
+
+// static
+int VideoDecodeStatsDBImpl::GetMaxDaysToKeepStats() {
+  return base::GetFieldTrialParamByFeatureAsDouble(
+      kMediaCapabilitiesWithParameters, kMaxDaysToKeepStatsParamName,
+      kMaxDaysToKeepStatsDefault);
+}
+
 // static
 std::unique_ptr<VideoDecodeStatsDBImpl> VideoDecodeStatsDBImpl::Create(
     base::FilePath db_dir) {
@@ -137,8 +163,11 @@ bool VideoDecodeStatsDBImpl::AreStatsExpired(
     last_write_date = default_write_time_.ToJsTime();
   }
 
+  const int kMaxDaysToKeepStats = GetMaxDaysToKeepStats();
+  DCHECK_GT(kMaxDaysToKeepStats, 0);
+
   return wall_clock_->Now() - base::Time::FromJsTime(last_write_date) >
-         base::TimeDelta::FromDays(VideoDecodeStatsDBImpl::kMaxDaysToKeepStats);
+         base::TimeDelta::FromDays(kMaxDaysToKeepStats);
 }
 
 void VideoDecodeStatsDBImpl::WriteUpdatedEntry(
@@ -170,6 +199,9 @@ void VideoDecodeStatsDBImpl::WriteUpdatedEntry(
   uint64_t old_frames_dropped = stats_proto->frames_dropped();
   uint64_t old_frames_power_efficient = stats_proto->frames_power_efficient();
 
+  const uint64_t kMaxFramesPerBuffer = GetMaxFramesPerBuffer();
+  DCHECK_GT(kMaxFramesPerBuffer, 0UL);
+
   if (old_frames_decoded + new_entry.frames_decoded > kMaxFramesPerBuffer) {
     // The |new_entry| is pushing out some or all of the old data. Achieve this
     // by weighting the dropped and power efficiency stats by the ratio of the

media/capabilities/video_decode_stats_db_impl.h

@@ -29,19 +29,8 @@ class DecodeStatsProto;
 // construction. API callbacks will also occur on this sequence.
 class MEDIA_EXPORT VideoDecodeStatsDBImpl : public VideoDecodeStatsDB {
  public:
-  enum : int {
-    // Number chosen after manual review of metrics (accuracy, precision,
-    // recall).
-    // TODO(chcunningham): Run experiments with different values. Metrics
-    // suggest different platforms, even different stream properties (e.g.
-    // framerate) could benefit from customized thresholds. Machine learning
-    // would probably be best.
-    kMaxFramesPerBuffer = 2500,
-    // Number of days after which stats will be discarded if not updated. This
-    // avoids users getting stuck with a bad capability prediction that may have
-    // been due to one-off circumstances.
-    kMaxDaysToKeepStats = 30,
-  };
+  static const char kMaxFramesPerBufferParamName[];
+  static const char kMaxDaysToKeepStatsParamName[];
 
   // Create an instance! |db_dir| specifies where to store LevelDB files to
   // disk. LevelDB generates a handful of files, so its recommended to provide a
@@ -74,6 +63,15 @@ class MEDIA_EXPORT VideoDecodeStatsDBImpl : public VideoDecodeStatsDB {
   // after the proto update hits the chrome Stable channel (M71).
   static constexpr char kDefaultWriteTime[] = "01-FEB-2019 12:00pm";
 
+  // Number of decoded frames to keep in the rolling "window" for a given entry
+  // in the database.
+  static int GetMaxFramesPerBuffer();
+
+  // Number of days after which stats will be discarded if not updated. This
+  // avoids users getting stuck with a bad capability prediction that may have
+  // been due to one-off circumstances.
+  static int GetMaxDaysToKeepStats();
+
   // Called when the database has been initialized. Will immediately call
   // |init_cb| to forward |success|.
   void OnInit(InitializeCB init_cb, bool success);
@@ -111,7 +109,7 @@ class MEDIA_EXPORT VideoDecodeStatsDBImpl : public VideoDecodeStatsDB {
   void OnStatsCleared(base::OnceClosure clear_done_cb, bool success);
 
   // Return true if:
-  //     "now" - stats_proto.last_write_date > kMaxDaysToKeepStats
+  //     "now" - stats_proto.last_write_date > GeMaxDaysToKeepStats()
   bool AreStatsExpired(const DecodeStatsProto* const stats_proto);
 
   void set_wall_clock_for_test(const base::Clock* tick_clock) {