[WIP]Create a V8 sampler library and tracing controller.

include/v8-sampler.h

Index: include/v8-sampler.h
diff --git a/include/v8-sampler.h b/include/v8-sampler.h
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+// 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_SAMPLER_H_
+#define V8_SAMPLER_H_
+
+#include "src/globals.h"
+#include "src/profiler/sampler.h"
+
+#if V8_OS_POSIX && !V8_OS_CYGWIN
+#define USE_SIGNALS
+#endif
+
+#if defined(ANDROID)
+  // Phones and tablets have processors that are much slower than desktop
+  // and laptop computers for which current heuristics are tuned.
+  static const int kSamplingIntervalMs = 5;
+#else
+  static const int kSamplingIntervalMs = 1;
+#endif
+
+namespace v8 {
+
+namespace internal {
+class Isolate;
+}
+
+class Isolate;
+class SamplerThread;
+#if defined(USE_SIGNALS)
+class SignalHandler;
+#endif
+
+class V8Sampler {
+ public:
+  // Initializes the sampler support. Called once at embedder startup.
+  static void SetUp();
+  static void TearDown();
+  static void SetInterval(int interval);
+
+  // Initialize sampler.
+  V8Sampler(Isolate* isolate);
+  virtual ~V8Sampler();
+
+  void CollectStackSample(const RegisterState& state,
+                          void** frames, size_t frames_limit,
+                          SampleInfo* sample_info);
+  void SetJitCodeEventHandler(JitCodeEventOptions,
+                              void* handler);
+
+  Isolate* isolate() const { return isolate_; }
+
+  // Performs stack sampling.
+  void SampleStack(const RegisterState& regs);
+
+  // Start and stop sampler.
+  void Start();
+  void Stop();
+
+  // Whether the sampling thread should use this Sampler for CPU profiling?
+  bool IsProfiling() const {
+    return base::NoBarrier_Load(&profiling_) > 0 &&
+        !base::NoBarrier_Load(&has_processing_thread_);
+  }
+  void IncreaseProfilingDepth();
+  void DecreaseProfilingDepth();
+
+  // Whether the sampler is running (that is, consumes resources).
+  bool IsActive() const { return base::NoBarrier_Load(&active_); }
+
+  void DoSample();
+  // If true next sample must be initiated on the profiler event processor
+  // thread right after latest sample is processed.
+  void SetHasProcessingThread(bool value) {
+    base::NoBarrier_Store(&has_processing_thread_, value);
+  }
+
+  // Used in tests to make sure that stack sampling is performed.
+  unsigned js_sample_count() const { return js_sample_count_; }
+  unsigned external_sample_count() const { return external_sample_count_; }
+  void StartCountingSamples() {
+    js_sample_count_ = 0;
+    external_sample_count_ = 0;
+    is_counting_samples_ = true;
+  }
+
+  class PlatformData;
+  PlatformData* platform_data() const { return data_; }
+
+ protected:
+  // This method is called for each sampling period with the current
+  // program counter.
+  virtual void Tick(i::TickSample* tick_sample) = 0;
+
+ private:
+  void SetActive(bool value) { base::NoBarrier_Store(&active_, value); }
+
+  Isolate* isolate_;
+  base::Atomic32 profiling_;
+  base::Atomic32 has_processing_thread_;
+  base::Atomic32 active_;
+  PlatformData* data_;  // Platform specific data.
+  // Counts stack samples taken in JS VM state.
+  bool is_counting_samples_;
+  unsigned js_sample_count_;
+  unsigned external_sample_count_;
+  DISALLOW_COPY_AND_ASSIGN(V8Sampler);
+  // DISALLOW_IMPLICIT_CONSTRUCTORS(V8Sampler);
+};
+
+}  // v8
+
+#endif  // V8_SAMPLER_H_