GitLab

This is a reland of https://chromium-review.googlesource.com/1130470.
The double end session issue was fixed by
https://chromium-review.googlesource.com/1136725.

Previously, a tab was proactively discarded when it had spent T time hidden,
where T depends on the number of non-discarded tabs and the amount of
physical memory. Unfortunately, that meant that if a user kept Chrome
open during the night without touching it, all hidden tabs were discarded
in the morning.

With this CL, we use the "Chrome usage time since hidden" to determine
if a tab should be proactively discarded. That will prevent the unwanted
behavior of finding all tabs discarded after a long period of inactivity.

TBR=sebmarchand@chromium.org

Bug: 775644
Change-Id: I57a08a47aad76087b54277d19849228e1ed00305
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Reviewed-on: https://chromium-review.googlesource.com/1136791
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575032}