AudioBufferSourceNode.buffer can only be set once.

Source/modules/webaudio/AudioBufferSourceNode.cpp

Index: Source/modules/webaudio/AudioBufferSourceNode.cpp
diff --git a/Source/modules/webaudio/AudioBufferSourceNode.cpp b/Source/modules/webaudio/AudioBufferSourceNode.cpp
index 5d40b0ae4c8941d76df1b7548b4005c980e23d54..1d98047e14eb1a91985e17c3ed718e365e515c4f 100644
--- a/Source/modules/webaudio/AudioBufferSourceNode.cpp
+++ b/Source/modules/webaudio/AudioBufferSourceNode.cpp
@@ -30,6 +30,7 @@
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/dom/ExceptionCode.h"
+#include "core/frame/UseCounter.h"
 #include "platform/audio/AudioUtilities.h"
 #include "modules/webaudio/AudioContext.h"
 #include "modules/webaudio/AudioNodeOutput.h"
@@ -340,6 +341,12 @@ void AudioBufferSourceNode::setBuffer(AudioBuffer* buffer, ExceptionState& excep
 {
     ASSERT(isMainThread());
 
+    if (m_buffer) {
+        // Setting the buffer more than once is deprecated.  Change this to a DOM exception in M45
+        // or so.
+        UseCounter::countDeprecation(context()->executionContext(), UseCounter::AudioBufferSourceBufferOnce);
+    }
+
     // The context must be locked since changing the buffer can re-configure the number of channels that are output.
     AudioContext::AutoLocker contextLocker(context());