More informative error messages for non-Transferables.

Source/bindings/v8/custom/V8DedicatedWorkerGlobalScopeCustom.cpp

Index: Source/bindings/v8/custom/V8DedicatedWorkerGlobalScopeCustom.cpp
diff --git a/Source/bindings/v8/custom/V8DedicatedWorkerGlobalScopeCustom.cpp b/Source/bindings/v8/custom/V8DedicatedWorkerGlobalScopeCustom.cpp
index ffa25a147a0b9f0e3bbc5aef81f5d19e157e8cbb..8994365f8878950e09fbbe3434e2b09a9ff7d5a2 100644
--- a/Source/bindings/v8/custom/V8DedicatedWorkerGlobalScopeCustom.cpp
+++ b/Source/bindings/v8/custom/V8DedicatedWorkerGlobalScopeCustom.cpp
@@ -31,6 +31,7 @@
 #include "config.h"
 #include "V8DedicatedWorkerGlobalScope.h"
 
+#include "bindings/v8/ExceptionMessages.h"
 #include "bindings/v8/ExceptionState.h"
 #include "bindings/v8/V8Binding.h"
 #include "bindings/v8/V8Utilities.h"
@@ -46,8 +47,12 @@ void V8DedicatedWorkerGlobalScope::postMessageMethodCustom(const v8::FunctionCal
     MessagePortArray ports;
     ArrayBufferArray arrayBuffers;
     if (args.Length() > 1) {
-        if (!extractTransferables(args[1], ports, arrayBuffers, args.GetIsolate()))
+        bool notASequence = false;
+        if (!extractTransferables(args[1], ports, arrayBuffers, notASequence, args.GetIsolate())) {
+            if (notASequence)
+                throwTypeError(ExceptionMessages::failedToExecute("postMessage", "WorkerGlobalScope", ExceptionMessages::notASequenceType("Second")), args.GetIsolate());
             return;
+        }
     }
     bool didThrow = false;
     RefPtr<SerializedScriptValue> message =