Fix PPB_Flash_MessageLoop.

This CL suspends script callbacks and resource loads while running nested message loop using PPB_Flash_MessageLoop.

BUG=569496

Review URL: https://codereview.chromium.org/1559113002

Cr-Commit-Position: refs/heads/master@{#374529}
  State() : result_(PP_OK), run_called_(false), quit_called_(false) {}

  State() : result_(PP_OK), run_called_(false), quit_called_(false) {}
