Change frame tracker's trace object type to stringstream

This CL changes the tracker's trace object to a stringstream, allowing
the logging of more types of data. This CL also takes advantage of said
feature to log |begin_main_frame_data_.previous_sequence| and
|args.sequence_number| in ReportBeginMainFrame() and
ReportMainFrameCausedNoDamage().

Bug: 1017291
Change-Id: I81330b10fa2347658587ee1f9e320fb185ae35cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1903609Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Mingjing Zhang <mjzhang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713621}

cc/metrics/frame_sequence_tracker.cc

@@ -17,11 +17,13 @@
 
 // This macro is used with DCHECK to provide addition debug info.
 #if DCHECK_IS_ON()
-#define TRACKER_DCHECK_MSG                                \
-  " in " << kFrameSequenceTrackerTypeNames[this->type_]   \
-         << " tracker: " << frame_sequence_trace_ << " (" \
-         << frame_sequence_trace_.size() << ")";
+#define TRACKER_TRACE_STREAM frame_sequence_trace_
+#define TRACKER_DCHECK_MSG                                      \
+  " in " << kFrameSequenceTrackerTypeNames[this->type_]         \
+         << " tracker: " << frame_sequence_trace_.str() << " (" \
+         << frame_sequence_trace_.str().size() << ")";
 #else
+#define TRACKER_TRACE_STREAM EAT_STREAM_PARAMETERS
 #define TRACKER_DCHECK_MSG ""
 #endif
 
@@ -293,7 +295,7 @@ void FrameSequenceTracker::ReportBeginImplFrame(
   if (ShouldIgnoreBeginFrameSource(args.source_id))
     return;
 
-  LogFrameSequenceTrace('b');
+  TRACKER_TRACE_STREAM << 'b';
   UpdateTrackedFrameData(&begin_impl_frame_data_, args.source_id,
                          args.sequence_number);
   impl_throughput_.frames_expected +=
@@ -311,7 +313,9 @@ void FrameSequenceTracker::ReportBeginMainFrame(
   if (ShouldIgnoreBeginFrameSource(args.source_id))
     return;
 
-  LogFrameSequenceTrace('B');
+  TRACKER_TRACE_STREAM << 'B';
+  TRACKER_TRACE_STREAM << "(" << begin_main_frame_data_.previous_sequence << ","
+                       << args.sequence_number << ")";
   UpdateTrackedFrameData(&begin_main_frame_data_, args.source_id,
                          args.sequence_number);
   if (first_received_main_sequence_ == 0)
@@ -345,7 +349,7 @@ void FrameSequenceTracker::ReportSubmitFrame(
       origin_args.sequence_number >= first_received_main_sequence_) {
     if (last_submitted_main_sequence_ == 0 ||
         origin_args.sequence_number > last_submitted_main_sequence_) {
-      LogFrameSequenceTrace('S');
+      TRACKER_TRACE_STREAM << 'S';
 
       last_submitted_main_sequence_ = origin_args.sequence_number;
       main_frames_.push_back(frame_token);
@@ -381,7 +385,7 @@ void FrameSequenceTracker::ReportFramePresented(
     return;
   }
 
-  LogFrameSequenceTrace('P');
+  TRACKER_TRACE_STREAM << 'P';
 
   TRACE_EVENT_ASYNC_STEP_INTO_WITH_TIMESTAMP0(
       "cc,benchmark", "FrameSequenceTracker", this, "FramePresented",
@@ -457,7 +461,7 @@ void FrameSequenceTracker::ReportImplFrameCausedNoDamage(
       ack.sequence_number < begin_impl_frame_data_.previous_sequence) {
     return;
   }
-  LogFrameSequenceTrace('n');
+  TRACKER_TRACE_STREAM << 'n';
   DCHECK_GT(impl_throughput_.frames_expected, 0u) << TRACKER_DCHECK_MSG;
   DCHECK_GT(impl_throughput_.frames_expected, impl_throughput_.frames_produced)
       << TRACKER_DCHECK_MSG;
@@ -482,7 +486,9 @@ void FrameSequenceTracker::ReportMainFrameCausedNoDamage(
     return;
   }
 
-  LogFrameSequenceTrace('N');
+  TRACKER_TRACE_STREAM << 'N';
+  TRACKER_TRACE_STREAM << "(" << begin_main_frame_data_.previous_sequence << ","
+                       << args.sequence_number << ")";
   DCHECK_GT(main_throughput_.frames_expected, 0u) << TRACKER_DCHECK_MSG;
   DCHECK_GT(main_throughput_.frames_expected, main_throughput_.frames_produced)
       << TRACKER_DCHECK_MSG;

cc/metrics/frame_sequence_tracker.h

@@ -182,12 +182,6 @@ class CC_EXPORT FrameSequenceTracker {
     termination_status_ = TerminationStatus::kScheduledForTermination;
   }
 
-  inline void LogFrameSequenceTrace(unsigned char letter) {
-#if DCHECK_IS_ON()
-    frame_sequence_trace_.push_back(letter);
-#endif
-  }
-
   struct TrackedFrameData {
     // Represents the |BeginFrameArgs::source_id| and
     // |BeginFrameArgs::sequence_number| fields of the last processed
@@ -292,15 +286,15 @@ class CC_EXPORT FrameSequenceTracker {
   const base::TimeDelta time_delta_to_report_ = base::TimeDelta::FromSeconds(5);
 
 #if DCHECK_IS_ON()
-  // This string represents a sequence of frame reporting activities on the
-  // current tracker. Each letter can be one of the following:
+  // This stringstream represents a sequence of frame reporting activities on
+  // the current tracker. Each letter can be one of the following:
   // {'B', 'N', 'b', 'n', 'S', 'P'}, where
   // 'B' = ReportBeginMainFrame(), 'N' = ReportMainFrameCausedNoDamage(),
   // 'b' = ReportBeginImplFrame(), 'n' = ReportMainFrameCausedNoDamage(),
   // 'S' = ReportSubmitFrame() and 'P' = ReportFramePresented().
   // Note that |frame_sequence_trace_| is only defined and populated
   // when DCHECK is on.
-  std::string frame_sequence_trace_;
+  std::stringstream frame_sequence_trace_;
 #endif
 };