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..95730ed72b834f5d0703b5aa454e78dfb39eb1bc 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 "webkitAudioContext is deprecated; use AudioContext instead";

[Ken Russell (switch to Gerrit), 2014/12/17 00:44:30]

Use replacedBy("webkitAudioContext", "AudioContext").

[Raymond Toy, 2014/12/17 05:53:08]

Done.

+
+    case PrefixedOfflineAudioContext:
+        return "webkitOfflineAudioContext is deprecated; use OfflineAudioContext instead";

[Ken Russell (switch to Gerrit), 2014/12/17 00:44:30]

Similar comment here.

[Raymond Toy, 2014/12/17 05:53:08]

Done.

+
     // Features that aren't deprecated don't have a deprecation message.
     default:
         return String();