Add counters for all of the WebAudio nodes and important methods.

Source/core/frame/UseCounter.cpp

Index: Source/core/frame/UseCounter.cpp
diff --git a/Source/core/frame/UseCounter.cpp b/Source/core/frame/UseCounter.cpp
index f94f926e5a5ed39d3a6a879053da52332f592286..48f7453f0409f561bdaa7340e9d41b88bbe7b255 100644
--- a/Source/core/frame/UseCounter.cpp
+++ b/Source/core/frame/UseCounter.cpp
@@ -833,6 +833,12 @@ String UseCounter::deprecationMessage(Feature feature)
     case PrefixedWindowURL:
         return replacedBy("webkitURL", "URL");
 
+    case PrefixedAudioContext:
+        return replacedBy("webkitAudioContext", "AudioContext");
+
+    case PrefixedOfflineAudioContext:
+        return replacedBy("webkitOfflineAudioContext", "OfflineAudioContext");
+
     // Features that aren't deprecated don't have a deprecation message.
     default:
         return String();