Attempt #2: Expose wasDiscarded after tab discard.

This is needed for Lifecycle API, see:
https://github.com/WICG/web-lifecycle
WasDiscarded is set on RequestNavigationParams on browser side and
passed into to WebURLRequest on renderer side. And later
set on the Document in DocumentLoader::CommitNavigation.

For detailed discussion, see (internal) thread:
https://groups.google.com/a/google.com/d/msg/chrome-lifecycle-apis/e0vsRLUISBE/t_BKYGcwAQAJ

Change-Id: I160628db6ba0a01f7b5281c78d7c2df40a28611f

BUG: chromium:816454
Change-Id: I160628db6ba0a01f7b5281c78d7c2df40a28611f
Reviewed-on: https://chromium-review.googlesource.com/912488
Commit-Queue: Shubhie Panicker <[email protected]>
Reviewed-by: Charlie Reis <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Alex Moshchuk <[email protected]>
Reviewed-by: Camille Lamy <[email protected]>
Reviewed-by: Jochen Eisinger <[email protected]>
Cr-Commit-Position: refs/heads/master@{#540997}
29 files changed