Enable startup profiling by Win x64 stack sampling profiler

base/profiler/stack_sampling_profiler.h

Index: base/profiler/stack_sampling_profiler.h
diff --git a/base/profiler/stack_sampling_profiler.h b/base/profiler/stack_sampling_profiler.h
index 44387868310f87ca3a6fde6b3914130f1c3af025..8594ca404d9d11933326dbcf8ec729cef9f56f97 100644
--- a/base/profiler/stack_sampling_profiler.h
+++ b/base/profiler/stack_sampling_profiler.h
@@ -31,11 +31,12 @@ namespace base {
 //   base::StackSamplingProfiler profiler(base::PlatformThread::CurrentId()),
 //       params);
 //
-//   // To process the profiles within Chrome rather than via UMA, set a custom
-//   // completed callback:
+//   // Or, to process the profiles within Chrome rather than via UMA, use a
+//   // custom completed callback:
 //   base::Callback<void(const std::vector<Profile>&)>
 //       thread_safe_callback = ...;
-//   profiler.SetCustomCompletedCallback(thread_safe_callback);
+//   base::StackSamplingProfiler profiler(base::PlatformThread::CurrentId()),
+//       params, thread_safe_callback);
 //
 //   profiler.Start();
 //   // ... work being done on the target thread here ...
@@ -43,11 +44,10 @@ namespace base {
 //
 // When all profiles are complete or the profiler is stopped, if the custom
 // completed callback was set it will be called from the profiler thread with
-// the completed profiles. If no callback was set, the profiles are stored
-// internally and retrieved for UMA through
-// GetPendingProfiles(). GetPendingProfiles() should never be called by other
-// code; to retrieve profiles for in-process processing, set a completed
-// callback.
+// the completed profiles. Otherwise, the default completed callback will be
+// called with the profiles. It is expected that the the default completed
+// callback is set by the metrics system to allow profiles to be provided via
+// UMA.
 class BASE_EXPORT StackSamplingProfiler {
  public:
   // Module represents the module (DLL or exe) corresponding to a stack frame.
@@ -153,8 +153,17 @@ class BASE_EXPORT StackSamplingProfiler {
     bool preserve_sample_ordering;
   };
 
+  // Callback function that accepts completed profiles.
+  using CompletedCallback = Callback<void(const std::vector<Profile>&)>;
+
+  // Creates a profiler that sends completed profiles to the default completed
+  // callback.
   StackSamplingProfiler(PlatformThreadId thread_id,
                         const SamplingParams& params);
+  // Creates a profiler that sends completed profiles to |completed_callback|.
+  StackSamplingProfiler(PlatformThreadId thread_id,
+                        const SamplingParams& params,
+                        CompletedCallback callback);
   ~StackSamplingProfiler();
 
   // Initializes the profiler and starts sampling.
@@ -164,19 +173,14 @@ class BASE_EXPORT StackSamplingProfiler {
   // bursts specified in the SamplingParams are completed.
   void Stop();
 
-  // Gets the pending profiles into *|profiles| and clears the internal
-  // storage. This function is thread safe.
+  // Sets a callback to process profiles collected by profiler instances without
+  // a completed callback. Profiles are queued internally until a non-null
+  // callback is provided to this function,
   //
-  // ***This is intended for use only by UMA.*** Callers who want to process the
-  // collected profiles should use SetCustomCompletedCallback.
-  static void GetPendingProfiles(std::vector<Profile>* profiles);
-
-  // By default, collected profiles are stored internally and can be retrieved
-  // by GetPendingProfiles. If a callback is provided via this function,
-  // however, it will be called with the collected profiles instead. Note that
-  // this call to the callback occurs *on the profiler thread*.
-  void SetCustomCompletedCallback(
-      Callback<void(const std::vector<Profile>&)> callback);
+  // The callback is typically called on a separate thread, so must be thread
+  // safe. If completed profiles are queued when set, it will also be called
+  // immediately on the calling thread.
+  static void SetDefaultCompletedCallback(CompletedCallback callback);
 
  private:
   class SamplingThread;
@@ -190,9 +194,8 @@ class BASE_EXPORT StackSamplingProfiler {
   const SamplingParams params_;
 
   scoped_ptr<SamplingThread, SamplingThreadDeleter> sampling_thread_;
-  scoped_ptr<NativeStackSampler> native_sampler_;
 
-  Callback<void(const std::vector<Profile>&)> custom_completed_callback_;
+  const CompletedCallback completed_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(StackSamplingProfiler);
 };