[DevTools] Various tweaks to inspector_protocol.

- allow importing all domains in single header;
- support for <includes.h>;
- separate export macro/header for lib, protocol and exported;
- improved code for defaults.

BUG=637032

Review-Url: https://codereview.chromium.org/2296043004
Cr-Commit-Position: refs/heads/master@{#415753}
15 files changed