headless: Implement convenience overloads for DevTools commands

Implement conveniene overloads for DevTools commands which only take
required parameters. For example, instead of this:

    client->GetPage()->Navigate(
        page::NavigateParams::Builder()
            .SetUrl("https://www.example.com"))
            .Build());

you can now do this:

    client->GetPage()->Navigate("https://www.example.com");

BUG=595353

Review URL: https://codereview.chromium.org/1906503002

Cr-Commit-Position: refs/heads/master@{#388527}
3 files changed