After r259781, debug hooks are now generated for all but the first sub-expression in a comma expression.

[Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp](http://trac.webkit.org/changeset/259781/webkit/trunk/Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp):
```
    RegisterID* CommaNode::emitBytecode(BytecodeGenerator& generator, RegisterID* dst)
    {
        for (; node->next(); node = node->next()) {
            generator.emitNode(generator.ignoredResult(), node->m_expr);

            // Don't emit a debug hook for the first expression, as that should've already happened in
            // the containing statement.
            generator.emitDebugHook(node->next()->m_expr);
        }
        return generator.emitNodeInTailPosition(dst, node->m_expr);
    }
```

This comment is inaccurate, as in the simple case of `true && (a(), b())`.