Quick: Fix marking high words in DCE.

This CL properly fixes the high word marking and reverts
which was just covering up the underlying issue. A unit test
for the encountered issue is provided, though it does not
expose the deficiency in the cover-up CL.

Bug: 20640451

(cherry picked from commit 9cacef6e811940c2f21e7e54055379a2c43f0d06)

Change-Id: I4c4ca82fe4b2e34feb38090d88a5d5c754914f89
2 files changed