[profiler] Introduce Tracing CPU profiler V8 API.

include/v8-profiler.h

 // Copyright 2010 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_V8_PROFILER_H_
 #define V8_V8_PROFILER_H_
 
 #include <vector>
 #include "v8.h"  // NOLINT(build/include)
 
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 };
 
 }  // namespace v8
 
 #ifdef V8_OS_WIN
 template class V8_EXPORT std::vector<v8::CpuProfileDeoptInfo>;
 #endif
 
 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
   // include the runtime function we're calling. Externally exposed tick
   // samples don't care.
   enum RecordCEntryFrame { kIncludeCEntryFrame, kSkipCEntryFrame };
 
   TickSample()
       : state(OTHER),
         pc(nullptr),
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   uint32_t index;  // Index of the time interval that was changed.
   uint32_t count;  // New value of count field for the interval with this index.
   uint32_t size;  // New value of size field for the interval with this index.
 };
 
 
 }  // namespace v8
 
 
 #endif  // V8_V8_PROFILER_H_