[bindings] Assert toDoubleSlow on v8::Value being a number.

Source/bindings/core/v8/V8Binding.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 515 matching lines @@
         return 0;
     if (!std::isfinite(numberValue)) {
         exceptionState.throwTypeError("The provided float value is non-finite.");
         return 0;
     }
     return numberValue;
 }
 
 double toDoubleSlow(v8::Handle<v8::Value> value, ExceptionState& exceptionState)
 {
+    ASSERT(!value->IsNumber());
     v8::Isolate* isolate = v8::Isolate::GetCurrent();
     v8::TryCatch block(isolate);
     double doubleValue = value->NumberValue();
     if (block.HasCaught()) {
         exceptionState.rethrowV8Exception(block.Exception());
         return 0;
     }
     return doubleValue;
 }
 
@@ skipping 540 matching lines @@
         attributes->append(value);
 }
 
 AttributesWithSideEffectOnGet::AttributeSet* AttributesWithSideEffectOnGet::attributesWithSideEffectOnGet()
 {
     DEFINE_STATIC_LOCAL(AttributeSet, attributes, ());
     return &attributes;
 }
 
 } // namespace blink