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diff --git a/mozglue/baseprofiler/core/ProfileBuffer.h b/mozglue/baseprofiler/core/ProfileBuffer.h
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+++ b/mozglue/baseprofiler/core/ProfileBuffer.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZ_PROFILE_BUFFER_H
+#define MOZ_PROFILE_BUFFER_H
+
+#include "ProfileBufferEntry.h"
+
+#include "BaseProfiler.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/PowerOfTwo.h"
+#include "mozilla/ProfileBufferChunkManagerSingle.h"
+#include "mozilla/ProfileChunkedBuffer.h"
+
+namespace mozilla {
+namespace baseprofiler {
+
+// Class storing most profiling data in a ProfileChunkedBuffer.
+//
+// This class is used as a queue of entries which, after construction, never
+// allocates. This makes it safe to use in the profiler's "critical section".
+class ProfileBuffer final {
+ public:
+  // ProfileBuffer constructor
+  // @param aBuffer The in-session ProfileChunkedBuffer to use as buffer
+  // manager.
+  explicit ProfileBuffer(ProfileChunkedBuffer& aBuffer);
+
+  ProfileChunkedBuffer& UnderlyingChunkedBuffer() const { return mEntries; }
+
+  bool IsThreadSafe() const { return mEntries.IsThreadSafe(); }
+
+  // Add |aEntry| to the buffer, ignoring what kind of entry it is.
+  // Returns the position of the entry.
+  uint64_t AddEntry(const ProfileBufferEntry& aEntry);
+
+  // Add to the buffer a sample start (ThreadId) entry for aThreadId.
+  // Returns the position of the entry.
+  uint64_t AddThreadIdEntry(BaseProfilerThreadId aThreadId);
+
+  void CollectCodeLocation(const char* aLabel, const char* aStr,
+                           uint32_t aFrameFlags, uint64_t aInnerWindowID,
+                           const Maybe<uint32_t>& aLineNumber,
+                           const Maybe<uint32_t>& aColumnNumber,
+                           const Maybe<ProfilingCategoryPair>& aCategoryPair);
+
+  // Maximum size of a frameKey string that we'll handle.
+  static const size_t kMaxFrameKeyLength = 512;
+
+  // Stream JSON for samples in the buffer to aWriter, using the supplied
+  // UniqueStacks object.
+  // Only streams samples for the given thread ID and which were taken at or
+  // after aSinceTime. If ID is 0, ignore the stored thread ID; this should only
+  // be used when the buffer contains only one sample.
+  // Return the thread ID of the streamed sample(s), or 0.
+  BaseProfilerThreadId StreamSamplesToJSON(SpliceableJSONWriter& aWriter,
+                                           BaseProfilerThreadId aThreadId,
+                                           double aSinceTime,
+                                           UniqueStacks& aUniqueStacks) const;
+
+  void StreamMarkersToJSON(SpliceableJSONWriter& aWriter,
+                           BaseProfilerThreadId aThreadId,
+                           const TimeStamp& aProcessStartTime,
+                           double aSinceTime,
+                           UniqueStacks& aUniqueStacks) const;
+  void StreamPausedRangesToJSON(SpliceableJSONWriter& aWriter,
+                                double aSinceTime) const;
+  void StreamProfilerOverheadToJSON(SpliceableJSONWriter& aWriter,
+                                    const TimeStamp& aProcessStartTime,
+                                    double aSinceTime) const;
+  void StreamCountersToJSON(SpliceableJSONWriter& aWriter,
+                            const TimeStamp& aProcessStartTime,
+                            double aSinceTime) const;
+
+  // Find (via |aLastSample|) the most recent sample for the thread denoted by
+  // |aThreadId| and clone it, patching in the current time as appropriate.
+  // Mutate |aLastSample| to point to the newly inserted sample.
+  // Returns whether duplication was successful.
+  bool DuplicateLastSample(BaseProfilerThreadId aThreadId,
+                           const TimeStamp& aProcessStartTime,
+                           Maybe<uint64_t>& aLastSample);
+
+  void DiscardSamplesBeforeTime(double aTime);
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
+  size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
+
+  void CollectOverheadStats(TimeDuration aSamplingTime, TimeDuration aLocking,
+                            TimeDuration aCleaning, TimeDuration aCounters,
+                            TimeDuration aThreads);
+
+  ProfilerBufferInfo GetProfilerBufferInfo() const;
+
+ private:
+  // Add |aEntry| to the provider ProfileChunkedBuffer.
+  // `static` because it may be used to add an entry to a `ProfileChunkedBuffer`
+  // that is not attached to a `ProfileBuffer`.
+  static ProfileBufferBlockIndex AddEntry(
+      ProfileChunkedBuffer& aProfileChunkedBuffer,
+      const ProfileBufferEntry& aEntry);
+
+  // Add a sample start (ThreadId) entry for aThreadId to the provided
+  // ProfileChunkedBuffer. Returns the position of the entry.
+  // `static` because it may be used to add an entry to a `ProfileChunkedBuffer`
+  // that is not attached to a `ProfileBuffer`.
+  static ProfileBufferBlockIndex AddThreadIdEntry(
+      ProfileChunkedBuffer& aProfileChunkedBuffer,
+      BaseProfilerThreadId aThreadId);
+
+  // The storage in which this ProfileBuffer stores its entries.
+  ProfileChunkedBuffer& mEntries;
+
+ public:
+  // `BufferRangeStart()` and `BufferRangeEnd()` return `uint64_t` values
+  // corresponding to the first entry and past the last entry stored in
+  // `mEntries`.
+  //
+  // The returned values are not guaranteed to be stable, because other threads
+  // may also be accessing the buffer concurrently. But they will always
+  // increase, and can therefore give an indication of how far these values have
+  // *at least* reached. In particular:
+  // - Entries whose index is strictly less that `BufferRangeStart()` have been
+  //   discarded by now, so any related data may also be safely discarded.
+  // - It is safe to try and read entries at any index strictly less than
+  //   `BufferRangeEnd()` -- but note that these reads may fail by the time you
+  //   request them, as old entries get overwritten by new ones.
+  uint64_t BufferRangeStart() const { return mEntries.GetState().mRangeStart; }
+  uint64_t BufferRangeEnd() const { return mEntries.GetState().mRangeEnd; }
+
+ private:
+  // Single pre-allocated chunk (to avoid spurious mallocs), used when:
+  // - Duplicating sleeping stacks (hence scExpectedMaximumStackSize).
+  // - Adding JIT info.
+  // - Streaming stacks to JSON.
+  // Mutable because it's accessed from non-multithreaded const methods.
+  mutable Maybe<ProfileBufferChunkManagerSingle> mMaybeWorkerChunkManager;
+  ProfileBufferChunkManagerSingle& WorkerChunkManager() const {
+    if (mMaybeWorkerChunkManager.isNothing()) {
+      // Only actually allocate it on first use. (Some ProfileBuffers are
+      // temporary and don't actually need this.)
+      mMaybeWorkerChunkManager.emplace(
+          ProfileBufferChunk::SizeofChunkMetadata() +
+          ProfileBufferChunkManager::scExpectedMaximumStackSize);
+    }
+    return *mMaybeWorkerChunkManager;
+  }
+
+  // Time from launch (us) when first sampling was recorded.
+  double mFirstSamplingTimeUs = 0.0;
+  // Time from launch (us) when last sampling was recorded.
+  double mLastSamplingTimeUs = 0.0;
+  // Sampling stats: Interval (us) between successive samplings.
+  ProfilerStats mIntervalsUs;
+  // Sampling stats: Total duration (us) of each sampling. (Split detail below.)
+  ProfilerStats mOverheadsUs;
+  // Sampling stats: Time (us) to acquire the lock before sampling.
+  ProfilerStats mLockingsUs;
+  // Sampling stats: Time (us) to discard expired data.
+  ProfilerStats mCleaningsUs;
+  // Sampling stats: Time (us) to collect counter data.
+  ProfilerStats mCountersUs;
+  // Sampling stats: Time (us) to sample thread stacks.
+  ProfilerStats mThreadsUs;
+};
+
+/**
+ * Helper type used to implement ProfilerStackCollector. This type is used as
+ * the collector for MergeStacks by ProfileBuffer. It holds a reference to the
+ * buffer, as well as additional feature flags which are needed to control the
+ * data collection strategy
+ */
+class ProfileBufferCollector final : public ProfilerStackCollector {
+ public:
+  ProfileBufferCollector(ProfileBuffer& aBuf, uint64_t aSamplePos,
+                         uint64_t aBufferRangeStart)
+      : mBuf(aBuf),
+        mSamplePositionInBuffer(aSamplePos),
+        mBufferRangeStart(aBufferRangeStart) {
+    MOZ_ASSERT(
+        mSamplePositionInBuffer >= mBufferRangeStart,
+        "The sample position should always be after the buffer range start");
+  }
+
+  // Position at which the sample starts in the profiler buffer (which may be
+  // different from the buffer in which the sample data is collected here).
+  Maybe<uint64_t> SamplePositionInBuffer() override {
+    return Some(mSamplePositionInBuffer);
+  }
+
+  // Profiler buffer's range start (which may be different from the buffer in
+  // which the sample data is collected here).
+  Maybe<uint64_t> BufferRangeStart() override {
+    return Some(mBufferRangeStart);
+  }
+
+  virtual void CollectNativeLeafAddr(void* aAddr) override;
+  virtual void CollectProfilingStackFrame(
+      const ProfilingStackFrame& aFrame) override;
+
+ private:
+  ProfileBuffer& mBuf;
+  uint64_t mSamplePositionInBuffer;
+  uint64_t mBufferRangeStart;
+};
+
+}  // namespace baseprofiler
+}  // namespace mozilla
+
+#endif