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diff --git a/dom/media/webaudio/blink/ReverbConvolver.cpp b/dom/media/webaudio/blink/ReverbConvolver.cpp
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+/*
+ * Copyright (C) 2010 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1.  Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ * 2.  Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
+ *     its contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ReverbConvolver.h"
+#include "ReverbConvolverStage.h"
+
+using namespace mozilla;
+
+namespace WebCore {
+
+const int InputBufferSize = 8 * 16384;
+
+// We only process the leading portion of the impulse response in the real-time
+// thread.  We don't exceed this length. It turns out then, that the background
+// thread has about 278msec of scheduling slop. Empirically, this has been found
+// to be a good compromise between giving enough time for scheduling slop, while
+// still minimizing the amount of processing done in the primary (high-priority)
+// thread. This was found to be a good value on Mac OS X, and may work well on
+// other platforms as well, assuming the very rough scheduling latencies are
+// similar on these time-scales.  Of course, this code may need to be tuned for
+// individual platforms if this assumption is found to be incorrect.
+const size_t RealtimeFrameLimit = 8192 + 4096  // ~278msec @ 44.1KHz
+                                  - WEBAUDIO_BLOCK_SIZE;
+// First stage will have size MinFFTSize - successive stages will double in
+// size each time until we hit the maximum size.
+const size_t MinFFTSize = 256;
+// If we are using background threads then don't exceed this FFT size for the
+// stages which run in the real-time thread.  This avoids having only one or
+// two large stages (size 16384 or so) at the end which take a lot of time
+// every several processing slices.  This way we amortize the cost over more
+// processing slices.
+const size_t MaxRealtimeFFTSize = 4096;
+
+ReverbConvolver::ReverbConvolver(const float* impulseResponseData,
+                                 size_t impulseResponseLength,
+                                 size_t maxFFTSize, size_t convolverRenderPhase,
+                                 bool useBackgroundThreads,
+                                 bool* aAllocationFailure)
+    : m_impulseResponseLength(impulseResponseLength),
+      m_accumulationBuffer(),
+      m_inputBuffer(InputBufferSize),
+      m_backgroundThread("ConvolverWorker"),
+      m_backgroundThreadMonitor("ConvolverMonitor"),
+      m_useBackgroundThreads(useBackgroundThreads),
+      m_wantsToExit(false),
+      m_moreInputBuffered(false) {
+  *aAllocationFailure = !m_accumulationBuffer.allocate(impulseResponseLength +
+                                                       WEBAUDIO_BLOCK_SIZE);
+  if (*aAllocationFailure) {
+    return;
+  }
+  // For the moment, a good way to know if we have real-time constraint is to
+  // check if we're using background threads. Otherwise, assume we're being run
+  // from a command-line tool.
+  bool hasRealtimeConstraint = useBackgroundThreads;
+
+  const float* response = impulseResponseData;
+  size_t totalResponseLength = impulseResponseLength;
+
+  // The total latency is zero because the first FFT stage is small enough
+  // to return output in the first block.
+  size_t reverbTotalLatency = 0;
+
+  size_t stageOffset = 0;
+  size_t stagePhase = 0;
+  size_t fftSize = MinFFTSize;
+  while (stageOffset < totalResponseLength) {
+    size_t stageSize = fftSize / 2;
+
+    // For the last stage, it's possible that stageOffset is such that we're
+    // straddling the end of the impulse response buffer (if we use stageSize),
+    // so reduce the last stage's length...
+    if (stageSize + stageOffset > totalResponseLength) {
+      stageSize = totalResponseLength - stageOffset;
+      // Use smallest FFT that is large enough to cover the last stage.
+      fftSize = MinFFTSize;
+      while (stageSize * 2 > fftSize) {
+        fftSize *= 2;
+      }
+    }
+
+    // This "staggers" the time when each FFT happens so they don't all happen
+    // at the same time
+    int renderPhase = convolverRenderPhase + stagePhase;
+
+    UniquePtr<ReverbConvolverStage> stage(new ReverbConvolverStage(
+        response, totalResponseLength, reverbTotalLatency, stageOffset,
+        stageSize, fftSize, renderPhase, &m_accumulationBuffer));
+
+    bool isBackgroundStage = false;
+
+    if (this->useBackgroundThreads() && stageOffset > RealtimeFrameLimit) {
+      m_backgroundStages.AppendElement(std::move(stage));
+      isBackgroundStage = true;
+    } else
+      m_stages.AppendElement(std::move(stage));
+
+    // Figure out next FFT size
+    fftSize *= 2;
+
+    stageOffset += stageSize;
+
+    if (hasRealtimeConstraint && !isBackgroundStage &&
+        fftSize > MaxRealtimeFFTSize) {
+      fftSize = MaxRealtimeFFTSize;
+      // Custom phase positions for all but the first of the realtime
+      // stages of largest size.  These spread out the work of the
+      // larger realtime stages.  None of the FFTs of size 1024, 2048 or
+      // 4096 are performed when processing the same block.  The first
+      // MaxRealtimeFFTSize = 4096 stage, at the end of the doubling,
+      // performs its FFT at block 7.  The FFTs of size 2048 are
+      // performed in blocks 3 + 8 * n and size 1024 at 1 + 4 * n.
+      const uint32_t phaseLookup[] = {14, 0, 10, 4};
+      stagePhase = WEBAUDIO_BLOCK_SIZE *
+                   phaseLookup[m_stages.Length() % ArrayLength(phaseLookup)];
+    } else if (fftSize > maxFFTSize) {
+      fftSize = maxFFTSize;
+      // A prime offset spreads out FFTs in a way that all
+      // available phase positions will be used if there are sufficient
+      // stages.
+      stagePhase += 5 * WEBAUDIO_BLOCK_SIZE;
+    } else if (stageSize > WEBAUDIO_BLOCK_SIZE) {
+      // As the stages are doubling in size, the next FFT will occur
+      // mid-way between FFTs for this stage.
+      stagePhase = stageSize - WEBAUDIO_BLOCK_SIZE;
+    }
+  }
+
+  // Start up background thread
+  // FIXME: would be better to up the thread priority here.  It doesn't need to
+  // be real-time, but higher than the default...
+  if (this->useBackgroundThreads() && m_backgroundStages.Length() > 0) {
+    if (!m_backgroundThread.Start()) {
+      NS_WARNING("Cannot start convolver thread.");
+      return;
+    }
+    m_backgroundThread.message_loop()->PostTask(NewNonOwningRunnableMethod(
+        "WebCore::ReverbConvolver::backgroundThreadEntry", this,
+        &ReverbConvolver::backgroundThreadEntry));
+  }
+}
+
+ReverbConvolver::~ReverbConvolver() {
+  // Wait for background thread to stop
+  if (useBackgroundThreads() && m_backgroundThread.IsRunning()) {
+    m_wantsToExit = true;
+
+    // Wake up thread so it can return
+    {
+      MonitorAutoLock locker(m_backgroundThreadMonitor);
+      m_moreInputBuffered = true;
+      m_backgroundThreadMonitor.Notify();
+    }
+
+    m_backgroundThread.Stop();
+  }
+}
+
+size_t ReverbConvolver::sizeOfIncludingThis(
+    mozilla::MallocSizeOf aMallocSizeOf) const {
+  size_t amount = aMallocSizeOf(this);
+  amount += m_stages.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  for (size_t i = 0; i < m_stages.Length(); i++) {
+    if (m_stages[i]) {
+      amount += m_stages[i]->sizeOfIncludingThis(aMallocSizeOf);
+    }
+  }
+
+  amount += m_backgroundStages.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  for (size_t i = 0; i < m_backgroundStages.Length(); i++) {
+    if (m_backgroundStages[i]) {
+      amount += m_backgroundStages[i]->sizeOfIncludingThis(aMallocSizeOf);
+    }
+  }
+
+  // NB: The buffer sizes are static, so even though they might be accessed
+  //     in another thread it's safe to measure them.
+  amount += m_accumulationBuffer.sizeOfExcludingThis(aMallocSizeOf);
+  amount += m_inputBuffer.sizeOfExcludingThis(aMallocSizeOf);
+
+  // Possible future measurements:
+  // - m_backgroundThread
+  // - m_backgroundThreadMonitor
+  return amount;
+}
+
+void ReverbConvolver::backgroundThreadEntry() {
+  while (!m_wantsToExit) {
+    // Wait for realtime thread to give us more input
+    m_moreInputBuffered = false;
+    {
+      MonitorAutoLock locker(m_backgroundThreadMonitor);
+      while (!m_moreInputBuffered && !m_wantsToExit)
+        m_backgroundThreadMonitor.Wait();
+    }
+
+    // Process all of the stages until their read indices reach the input
+    // buffer's write index
+    int writeIndex = m_inputBuffer.writeIndex();
+
+    // Even though it doesn't seem like every stage needs to maintain its own
+    // version of readIndex we do this in case we want to run in more than one
+    // background thread.
+    int readIndex;
+
+    while ((readIndex = m_backgroundStages[0]->inputReadIndex()) !=
+           writeIndex) {  // FIXME: do better to detect buffer overrun...
+      // Accumulate contributions from each stage
+      for (size_t i = 0; i < m_backgroundStages.Length(); ++i)
+        m_backgroundStages[i]->processInBackground(this);
+    }
+  }
+}
+
+void ReverbConvolver::process(const float* sourceChannelData,
+                              float* destinationChannelData) {
+  const float* source = sourceChannelData;
+  float* destination = destinationChannelData;
+  bool isDataSafe = source && destination;
+  MOZ_ASSERT(isDataSafe);
+  if (!isDataSafe) return;
+
+  // Feed input buffer (read by all threads)
+  m_inputBuffer.write(source, WEBAUDIO_BLOCK_SIZE);
+
+  // Accumulate contributions from each stage
+  for (size_t i = 0; i < m_stages.Length(); ++i) m_stages[i]->process(source);
+
+  // Finally read from accumulation buffer
+  m_accumulationBuffer.readAndClear(destination, WEBAUDIO_BLOCK_SIZE);
+
+  // Now that we've buffered more input, wake up our background thread.
+
+  // Not using a MonitorAutoLock looks strange, but we use a TryLock() instead
+  // because this is run on the real-time thread where it is a disaster for the
+  // lock to be contended (causes audio glitching).  It's OK if we fail to
+  // signal from time to time, since we'll get to it the next time we're called.
+  // We're called repeatedly and frequently (around every 3ms).  The background
+  // thread is processing well into the future and has a considerable amount of
+  // leeway here...
+  if (m_backgroundThreadMonitor.TryLock()) {
+    m_moreInputBuffered = true;
+    m_backgroundThreadMonitor.Notify();
+    m_backgroundThreadMonitor.Unlock();
+  }
+}
+
+}  // namespace WebCore