GitLab

mojom::PrerenderProcessor::Abandon() is a mojo call from a renderer
process to the browser process in order to abandon a running prerender,
but this is never called. This CL removes the mojo function and relevant
functions (e.g., pre-finalizer).

> Why is this never called?

Abandon() is supposed to be called when a page that has
<link rel=prerender> navigates away, etc, and apparently
blink::PrerenderHandle::Dispose() calls it. However, actually Dispose()
never calls Abandon(). See the following code snippet.

  void PrerenderHandle::Dispose() {
    if (remote_processor_.is_bound() &&
        !GetExecutionContext()->IsContextDestroyed())
      remote_processor_->Abandon();
    Detach();
  }

Dispose() is called by ContextLifecycleObserver during the context
destruction. |remote_processor_| can be unbound at this point because
the remote processor is retained with MojoHeapRemote that is supposed
to be reset by ContextLifecycleObserver. There is an ordering issue
here. Also, even if the remote processor is still bound,
IsContextDestroyed() always returns true because Dispose() is called
during the context destruction.

In another case, Dispose() is called on the pre-finalizer, but this
doesn't work as well because PrerenderHandle::Cancel() that resets
|remote_processor_| or ContextDestroyed() that calls Dispose() are
already called before the pre-finalizer.

In summary, both Abandon() and the pre-finalizer are not necessary.
This CL removes them.

> Mojo connections are managed by MojoHeap variants. Does
> PrerenderHandle have to explicitly reset them on the context
> destruction?

That's not necessary. MojoHeap variants automatically reset the
connections on the context destruction. This CL removes
ContextLifecycleObserver implementation used for resetting the
connections from PrerenderHandle.

> Is the browser-side abandon code also never used?

No, it's used. Instead of waiting for Abandon() call from a renderer
process, PrerenderLinkManager::LinkPrerender in the browser process
monitors the connection of mojom::PrerenderProcessorClient and abandons
the running prerender on connection destruction. Therefore, this CL
doesn't remove the browser-side code.

Bug: 1130360
Change-Id: I14555530f98d1fb191b04f387636f58a52484c95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462987
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816897}