[DevTools] Copy objects from debugger context to inspected context properly.

BUG=637594

Review-Url: https://codereview.chromium.org/2253643002
Cr-Commit-Position: refs/heads/master@{#412436}
V8StackTraceImpl* V8Debugger::currentAsyncCallChain()
{
    if (!m_currentStacks.size())
        return nullptr;
    return m_currentStacks.back().get();
}

V8StackTraceImpl* V8Debugger::currentAsyncCallChain()
{
    if (!m_currentStacks.size())
        return nullptr;
    return m_currentStacks.back().get();
}
