Save heap object tracking data in heap snapshot

src/heap-snapshot-generator.cc

Index: src/heap-snapshot-generator.cc
diff --git a/src/heap-snapshot-generator.cc b/src/heap-snapshot-generator.cc
index 5864ad9b43fb9e82cf55b8e35a0bd0a3749d3ee7..ce9d705cd5e5730a2424a5ac87963474bd623191 100644
--- a/src/heap-snapshot-generator.cc
+++ b/src/heap-snapshot-generator.cc
@@ -2743,6 +2743,11 @@ void HeapSnapshotJSONSerializer::SerializeImpl() {
   if (writer_->aborted()) return;
   writer_->AddString("],\n");
 
+  writer_->AddString("\"samples\":[");
+  SerializeSamples();
+  if (writer_->aborted()) return;
+  writer_->AddString("],\n");
+
   writer_->AddString("\"strings\":[");
   SerializeStrings();
   if (writer_->aborted()) return;
@@ -2939,7 +2944,10 @@ void HeapSnapshotJSONSerializer::SerializeSnapshot() {
         JSON_S("function_info_index") ","
         JSON_S("count") ","
         JSON_S("size") ","
-        JSON_S("children"))));
+        JSON_S("children")) ","
+    JSON_S("sample_fields") ":" JSON_A(
+        JSON_S("timstamp_ms") ","
+        JSON_S("next_object_id"))));
 #undef JSON_S
 #undef JSON_O
 #undef JSON_A
@@ -2954,6 +2962,10 @@ void HeapSnapshotJSONSerializer::SerializeSnapshot() {
     count = tracker->function_info_list().length();
   }
   writer_->AddNumber(count);
+  writer_->AddString(",\"sample_count\":");
+  const List<HeapObjectsMap::TimeInterval>& samples =
+      snapshot_->profiler()->heap_object_map()->samples();
+  writer_->AddNumber(samples.length());
 }
 
 
@@ -3057,6 +3069,38 @@ void HeapSnapshotJSONSerializer::SerializeTraceNodeInfos() {
 }
 
 
+void HeapSnapshotJSONSerializer::SerializeSamples() {
+  const List<HeapObjectsMap::TimeInterval>& samples =
+      snapshot_->profiler()->heap_object_map()->samples();
+  if (samples.is_empty()) return;
+  base::TimeTicks start_time = samples[0].timestamp;
+  // The buffer needs space for 2 unsigned ints, 2 commas, \n and \0
+  const int kBufferSize =
+      2 * MaxDecimalDigitsIn<sizeof(
+              base::TimeDelta().InMilliseconds())>::kUnsigned  // NOLINT

[alph, 2015/03/19 14:05:27]

one is timedelta, another is id. these are two different types.

[yurys, 2015/03/19 14:13:26]

Done.

+      +
+      2 + 1 + 1;
+  EmbeddedVector<char, kBufferSize> buffer;
+  bool first_entry = true;
+  for (int i = 0; i < samples.length(); i++) {
+    HeapObjectsMap::TimeInterval& sample = samples[i];
+    int buffer_pos = 0;
+    if (first_entry) {

[alph, 2015/03/19 14:05:27]

i != 0

[yurys, 2015/03/19 14:13:26]

Done.

+      first_entry = false;
+    } else {
+      buffer[buffer_pos++] = ',';
+    }
+    base::TimeDelta time_delta = sample.timestamp - start_time;
+    buffer_pos = utoa(time_delta.InMilliseconds(), buffer, buffer_pos);

[alph, 2015/03/19 14:05:27]

Let's use microseconds as we do in cpu profiler to be consistent. wdyt?

[yurys, 2015/03/19 14:13:26]

Done.

+    buffer[buffer_pos++] = ',';
+    buffer_pos = utoa(sample.id, buffer, buffer_pos);
+    buffer[buffer_pos++] = '\n';
+    buffer[buffer_pos++] = '\0';
+    writer_->AddString(buffer.start());
+  }
+}
+
+
 void HeapSnapshotJSONSerializer::SerializeString(const unsigned char* s) {
   writer_->AddCharacter('\n');
   writer_->AddCharacter('\"');