[profiler] Introduce Tracing CPU profiler V8 API.

Tracing CPU profiler allows V8 to automatically collect CPU profile when tracing
is started with category v8.cpu_profile2 enabled.

BUG=chromium:406277

Review-Url: https://codereview.chromium.org/2378143003
Cr-Commit-Position: refs/heads/master@{#39855}

BUILD.gn

@@ -1535,6 +1535,8 @@ v8_source_set("v8_base") {
     "src/profiler/strings-storage.h",
     "src/profiler/tick-sample.cc",
     "src/profiler/tick-sample.h",
+    "src/profiler/tracing-cpu-profiler.cc",
+    "src/profiler/tracing-cpu-profiler.h",
     "src/profiler/unbound-queue-inl.h",
     "src/profiler/unbound-queue.h",
     "src/property-descriptor.cc",

include/v8-profiler.h

@@ -46,6 +46,20 @@ template class V8_EXPORT std::vector<v8::CpuProfileDeoptInfo>;
 
 namespace v8 {
 
+/**
+ * TracingCpuProfiler monitors tracing being enabled/disabled
+ * and emits CpuProfile trace events once v8.cpu_profile2 tracing category
+ * is enabled. It has no overhead unless the category is enabled.
+ */
+class V8_EXPORT TracingCpuProfiler {
+ public:
+  static std::unique_ptr<TracingCpuProfiler> Create(Isolate*);
+  virtual ~TracingCpuProfiler() = default;
+
+ protected:
+  TracingCpuProfiler() = default;
+};
+
 // TickSample captures the information collected for each sample.
 struct TickSample {
   // Internal profiling (with --prof + tools/$OS-tick-processor) wants to

src/profiler/tracing-cpu-profiler.cc

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/profiler/tracing-cpu-profiler.h"
+
+#include "src/v8.h"
+
+namespace v8 {
+
+std::unique_ptr<TracingCpuProfiler> TracingCpuProfiler::Create(
+    v8::Isolate* isolate) {
+  return std::unique_ptr<TracingCpuProfiler>(
+      new internal::TracingCpuProfilerImpl(
+          reinterpret_cast<internal::Isolate*>(isolate)));
+}
+
+namespace internal {
+
+TracingCpuProfilerImpl::TracingCpuProfilerImpl(Isolate* isolate) {}
+
+TracingCpuProfilerImpl::~TracingCpuProfilerImpl() {}
+
+}  // namespace internal
+}  // namespace v8

src/profiler/tracing-cpu-profiler.h

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_PROFILER_TRACING_CPU_PROFILER_H
+#define V8_PROFILER_TRACING_CPU_PROFILER_H
+
+#include "include/v8-profiler.h"
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace internal {
+
+class TracingCpuProfilerImpl final : public TracingCpuProfiler {
+ public:
+  explicit TracingCpuProfilerImpl(Isolate*);
+  ~TracingCpuProfilerImpl();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TracingCpuProfilerImpl);
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_PROFILER_TRACING_CPU_PROFILER_H

src/v8.gyp

@@ -1103,6 +1103,8 @@
         'profiler/strings-storage.h',
         'profiler/tick-sample.cc',
         'profiler/tick-sample.h',
+        'profiler/tracing-cpu-profiler.cc',
+        'profiler/tracing-cpu-profiler.h',
         'profiler/unbound-queue-inl.h',
         'profiler/unbound-queue.h',
         'property-descriptor.cc',