Avoid slow AudioParam automation path when possible

third_party/WebKit/Source/modules/webaudio/GainNode.cpp

 /*
  * 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
@@ skipping 49 matching lines @@
     } else {
         AudioBus* inputBus = input(0).bus();
 
         if (m_gain->hasSampleAccurateValues()) {
             // Apply sample-accurate gain scaling for precise envelopes, grain windows, etc.
             ASSERT(framesToProcess <= m_sampleAccurateGainValues.size());
             if (framesToProcess <= m_sampleAccurateGainValues.size()) {
                 float* gainValues = m_sampleAccurateGainValues.data();
                 m_gain->calculateSampleAccurateValues(gainValues, framesToProcess);
                 outputBus->copyWithSampleAccurateGainValuesFrom(*inputBus, gainValues, framesToProcess);
+                // Update m_lastGain so if the timeline ever ends, we get
+                // consistent data for the smoothing below.  (Without this,
+                // m_lastGain was the last value before the timeline started
+                // procesing.
+                m_lastGain = gainValues[framesToProcess - 1];
             }
         } else {
             // Apply the gain with de-zippering into the output bus.
             if (!m_lastGain && m_lastGain == m_gain->value()) {
                 // If the gain is 0 (and we've converged on dezippering), just zero the bus and set
                 // the silence hint.
                 outputBus->zero();
             } else {
                 outputBus->copyWithGainFrom(*inputBus, &m_lastGain, m_gain->value());
             }
@@ skipping 59 matching lines @@
 }
 
 DEFINE_TRACE(GainNode)
 {
     visitor->trace(m_gain);
     AudioNode::trace(visitor);
 }
 
 } // namespace blink