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Otherwise we lose track of display layout. In particular this is a
problem when dealing with software mirror mode since the state goes out
of sync and the second monitor will have the same origin as the primary
even though it's supposed to be right-of primary.

Follow-up to https://codereview.chromium.org/1129923004/ to fix software
mirror mode.

BUG=484294
TEST=Test software mirror mode and make sure it works

Review URL: https://codereview.chromium.org/1140773003

Cr-Commit-Position: refs/heads/master@{#329717}