GitLab

Builds the Surface tree considering Surfaces that correspond to
RootFrameSinks and detached Surfaces as root Surfaces. All of these are
attached to RootElement.

Bug:816802

TBR=sadrul@chromium.org

Change-Id: I74d11ddb0fed9dc31712dc6e98cf20e936856400
Reviewed-on: https://chromium-review.googlesource.com/1185964
Commit-Queue: Yi Xu <yiyix@chromium.org>
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589302}