[profiler] Update cpu profile tracing format.

Encapsulate nodes and samples into cpuProfile object.

BUG=chromium:406277

Review-Url: https://chromiumcodereview.appspot.com/2425093002
Cr-Commit-Position: refs/heads/master@{#40447}

src/profiler/profile-generator.cc

@@ -412,7 +412,7 @@ CpuProfile::CpuProfile(CpuProfiler* profiler, const char* title,
   value->SetDouble("startTime",
                    (start_time_ - base::TimeTicks()).InMicroseconds());
   TRACE_EVENT_SAMPLE_WITH_ID1(TRACE_DISABLED_BY_DEFAULT("v8.cpu_profiler"),
-                              "CpuProfile", this, "data", std::move(value));
+                              "Profile", this, "data", std::move(value));
 }
 
 void CpuProfile::AddPath(base::TimeTicks timestamp,
@@ -466,22 +466,27 @@ void CpuProfile::StreamPendingTraceEvents() {
   if (pending_nodes.empty() && !samples_.length()) return;
   auto value = TracedValue::Create();
 
-  if (!pending_nodes.empty()) {
-    value->BeginArray("nodes");
-    for (auto node : pending_nodes) {
-      value->BeginDictionary();
-      BuildNodeValue(node, value.get());
-      value->EndDictionary();
+  if (!pending_nodes.empty() || streaming_next_sample_ != samples_.length()) {
+    value->BeginDictionary("cpuProfile");
+    if (!pending_nodes.empty()) {
+      value->BeginArray("nodes");
+      for (auto node : pending_nodes) {
+        value->BeginDictionary();
+        BuildNodeValue(node, value.get());
+        value->EndDictionary();
+      }
+      value->EndArray();
     }
-    value->EndArray();
+    if (streaming_next_sample_ != samples_.length()) {
+      value->BeginArray("samples");
+      for (int i = streaming_next_sample_; i < samples_.length(); ++i) {
+        value->AppendInteger(samples_[i]->id());
+      }
+      value->EndArray();
+    }
+    value->EndDictionary();
   }
-
   if (streaming_next_sample_ != samples_.length()) {
-    value->BeginArray("samples");
-    for (int i = streaming_next_sample_; i < samples_.length(); ++i) {
-      value->AppendInteger(samples_[i]->id());
-    }
-    value->EndArray();
     value->BeginArray("timeDeltas");
     base::TimeTicks lastTimestamp =
         streaming_next_sample_ ? timestamps_[streaming_next_sample_ - 1]
@@ -497,8 +502,7 @@ void CpuProfile::StreamPendingTraceEvents() {
   }
 
   TRACE_EVENT_SAMPLE_WITH_ID1(TRACE_DISABLED_BY_DEFAULT("v8.cpu_profiler"),
-                              "CpuProfileChunk", this, "data",
-                              std::move(value));
+                              "ProfileChunk", this, "data", std::move(value));
 }
 
 void CpuProfile::FinishProfile() {
@@ -507,8 +511,7 @@ void CpuProfile::FinishProfile() {
   auto value = TracedValue::Create();
   value->SetDouble("endTime", (end_time_ - base::TimeTicks()).InMicroseconds());
   TRACE_EVENT_SAMPLE_WITH_ID1(TRACE_DISABLED_BY_DEFAULT("v8.cpu_profiler"),
-                              "CpuProfileChunk", this, "data",
-                              std::move(value));
+                              "ProfileChunk", this, "data", std::move(value));
 }
 
 void CpuProfile::Print() {

test/cctest/test-cpu-profiler.cc

@@ -2111,8 +2111,8 @@ namespace {
 class CpuProfileEventChecker : public v8::platform::tracing::TraceWriter {
  public:
   void AppendTraceEvent(TraceObject* trace_event) override {
-    if (trace_event->name() != std::string("CpuProfile") &&
-        trace_event->name() != std::string("CpuProfileChunk"))
+    if (trace_event->name() != std::string("Profile") &&
+        trace_event->name() != std::string("ProfileChunk"))
       return;
     CHECK(!profile_id_ || trace_event->id() == profile_id_);
     CHECK_EQ(1, trace_event->num_args());