[4/4] Process clearBrowserCahce/cookies commands in browser.

BUG=366585

Review URL: https://codereview.chromium.org/251183005

git-svn-id: svn://svn.chromium.org/blink/trunk@172984 bbb929c8-8fbe-4397-9dbb-9b2b20218538
void WebDevToolsAgentImpl::reattach(const WebString& savedState)
{
    if (m_attached)
        return;

    inspectorController()->reuseFrontend(this, savedState);
    blink::Platform::current()->currentThread()->addTaskObserver(this);
    m_attached = true;
}

void WebDevToolsAgentImpl::reattach(const WebString& savedState)
{
    if (m_attached)
        return;

    inspectorController()->reuseFrontend(this, savedState);
    blink::Platform::current()->currentThread()->addTaskObserver(this);
    m_attached = true;
}
