Implement StereoPannerNode for robust stereo panning

Source/platform/audio/Spatializer.h

Index: Source/platform/audio/Spatializer.h
diff --git a/Source/platform/audio/Spatializer.h b/Source/platform/audio/Spatializer.h
new file mode 100644
index 0000000000000000000000000000000000000000..aaa6ca34ad0bec5905a4bc96d84f6e2a3cb05d35
--- /dev/null
+++ b/Source/platform/audio/Spatializer.h
@@ -0,0 +1,47 @@
+// Copyright 2014 The Chromium 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 Spatializer_h
+#define Spatializer_h
+
+#include "platform/PlatformExport.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class AudioBus;
+
+// Abstract base class for spatializing a mono or stereo source.
+class PLATFORM_EXPORT Spatializer : public GarbageCollected<Spatializer> {
+public:
+    enum {
+        PanningModelEqualPower = 0
+
+        // We have a plan to add more panning models other than equal-power.
+        // (such as binaural-HRTF or N-channel surround panning)
+    };
+
+    typedef unsigned PanningModel;
+
+    static Spatializer* create(PanningModel, float sampleRate);
+
+    // Handle sample-accurate panning by AudioParam automation.
+    virtual void panWithSampleAccurateValues(const AudioBus* inputBus, AudioBus* outputBuf, const float* panValues, size_t framesToProcess) = 0;
+
+    // Handle de-zippered panning to a target value.
+    virtual void panToTargetValue(const AudioBus* inputBus, AudioBus* outputBuf, float panValue, size_t framesToProcess) = 0;
+
+    virtual void reset() = 0;
+    virtual double tailTime() const = 0;
+    virtual double latencyTime() const = 0;
+
+    virtual void trace(Visitor*) { }
+
+protected:
+    explicit Spatializer(PanningModel model) { }
+};
+
+} // namespace blink
+
+#endif // Spatializer_h