Add more informative messages for DOM exceptions.

Source/modules/webaudio/AudioBuffer.cpp

Index: Source/modules/webaudio/AudioBuffer.cpp
diff --git a/Source/modules/webaudio/AudioBuffer.cpp b/Source/modules/webaudio/AudioBuffer.cpp
index e41ba22063db137dd7ad7ee09439bec5b09c7465..ab9b5541c9a45beb51284a93e416d4c230591eee 100644
--- a/Source/modules/webaudio/AudioBuffer.cpp
+++ b/Source/modules/webaudio/AudioBuffer.cpp
@@ -32,6 +32,7 @@
 
 #include "modules/webaudio/AudioBuffer.h"
 
+#include "bindings/v8/ExceptionMessages.h"
 #include "bindings/v8/ExceptionState.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/platform/audio/AudioBus.h"
@@ -97,7 +98,12 @@ void AudioBuffer::releaseMemory()
 PassRefPtr<Float32Array> AudioBuffer::getChannelData(unsigned channelIndex, ExceptionState& es)
 {
     if (channelIndex >= m_channels.size()) {
-        es.throwUninformativeAndGenericDOMException(SyntaxError);
+        es.throwDOMException(
+            SyntaxError,
+            ExceptionMessages::failedToGet(
+                "getChannelData",

[Mike West, 2013/09/27 06:44:39]

If this is called as `ab.getChannelData()`, then I'd prefer
'ExceptionMessages::failedToExecute'. 'failedToGet' implies direct property
access, which I don't think this maps to.

+                "AudioBuffer",
+                "invalid channel index."));

[Mike West, 2013/09/27 06:44:39]

How about "The provided index (" + String::number(channelIndex) + ") is
invalid."?

         return 0;
     }