commit 89f07c0538eed5edb94f86582716b6b9b21d1e07
author Evan Birenbaum <birenbaum@google.com> Sat Jan 18 02:25:37 2020 +0000
committer CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org> Sat Jan 18 02:25:37 2020 +0000
tree 35bf948018f82dc5e5638a7ceb6447636e4983da
parent 801108c9aee69657eacb6d60a94735636426f857

[scenic] Add ObjectLinker::Link::ReleaseToken().

The new Flatland API functions for releasing a parent or child link also return
the link token to the caller so that a new link can be established. Right now,
the ObjectLinker consumes these tokens, but as soon as the link is resolved,
the tokens are discarded.

This change:
1. Makes the ObjectLinker hold onto the tokens in the resolved Endpoint rather
   than discarding them on link resolution.
2. Adds a function that allows the link holder to release the token.

When a link releases its token, it is invalidated, which results in the
link_invalidated callback being called if the link was initialized. If the link
was resolved, meaning it has an initialized peer, the peer will be
"unresolved". Unresolving a peer means:
1. The peer's link_invalidated callback will be called, but not erased.
2. The peer will be put back into the "initialized" state, meaning it retains
   its token and callbacks.

Even though the peer receives the link_invalidated callback, it does not need
to be initialized again. For example, if the released token is then used to
create a new link, the peer will receive the link_resolved callback again. This
means that any state set up in the link_resolved callback should be torn down
in the link_invalidated callback.

Fixed: 43745

TEST=fx shell runtests -t gfx_unittests

Change-Id: I3d27702e611402de22c2a99dc68f1fc07e51f374