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This fix is necessary to enable by default the iPad tab switcher.
It is a partial reland of https://codereview.chromium.org/1725533004

This CL:
-Always register/deregister for notifications.
-Centralizes the logic to use a LRU cache.
-Centralizes the logic to use an in-memory cache.
-Replaces msarda with jif in OWNERS.
-Triggers memory warning instead of calling |handleLowMemory| from tests.

BUG=None

Review-Url: https://codereview.chromium.org/2394253002
Cr-Commit-Position: refs/heads/master@{#427302}