GitLab

Introduces HeapMojoReceiverSet which is a wrapper around mojo::ReceiverSet.
And uses it for ManifestManager.

Bug: 1052319
Change-Id: I683567f0352c9b60811263a662bda85e31299426
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2063615
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743049}