Experiment for showing the Tab Switcher on returning to Chrome.

Adding a utility class to handle the logic of calculating if enough time
has passed. The last backgrounded time is already tracked in
ChromeTabbedActivity::onStopWithNative().

Experiment name is enable-tab-switcher-on-return. See `chrome://flags`

Available options are 30 or 60 minutes.

[email protected]

Bug: 898685
Change-Id: I916eb86b55525f06335d27cec84de78b1e366e98
Reviewed-on: https://chromium-review.googlesource.com/c/1384658
Reviewed-by: Avi Drissman <[email protected]>
Reviewed-by: Yusuf Ozuysal <[email protected]>
Commit-Queue: Matt Simmons <[email protected]>
Cr-Commit-Position: refs/heads/master@{#618309}
11 files changed