Test for save-page-as in presence of OOPIFs / site-per-process.
Test for save-page-as in presence of OOPIFs / site-per-process.

This CL adds a test that saves a page with cross-site iframes.
This test can repro a crash when the browser runs with --site-per-process flag
(setting this command line flag is currently commented out in the test;
this flag will be enabled once crbug.com/526786 is fully fixed).

This CL also opportunistically refactors some duplicated test code
into a new SaveCurrentTab helper method.

BUG=526786

Review URL: https://codereview.chromium.org/1323113002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#347245}

CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend