Fixes flickering in chrome://settings/startup with the scheduler enabled
Previously CustomHomePagesTableModel::SetToCurrentlyOpenPages was
sending a large number of StartupOverlay.updateStartupPages with
intermediate state as pre-existing rows where removed and then new ones
added and their titles looked up. This became a problem with the blink
scheduler enabled on touch devices, because a touch puts the renderer
scheduler into compositor priority and generated more frames than before
leading to horrible flickering of the dialog.
This patch fixes that by only sending a single update once all of the
titles have been looked up.
BUG=450953
Review URL: https://codereview.chromium.org/
870563003
Cr-Commit-Position: refs/heads/master@{#312695}