The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/293382aa925f692808d148b593b91f0a97aba739

commit 293382aa925f692808d148b593b91f0a97aba739
Author: Malay Keshav <malaykeshav@chromium.org>
Date: Tue Jun 12 20:06:39 2018

Add 2.0 DSF for external 4k display only if the display zoom is disabled

Display zoom is responsible for scaling when the flag is enabled so we
dont need to manualy set the device scale factor for external 4k
displays.

Bug:  851701 
Change-Id: I7b2789fa233dda89d3f2dd5031b5507c4c64b1ed
Component: Display Change Observer, 4k, Scaling
Reviewed-on: https://chromium-review.googlesource.com/1096343
Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566541}
[modify] https://crrev.com/293382aa925f692808d148b593b91f0a97aba739/services/ui/display/screen_manager_ozone_internal_unittests.cc
[modify] https://crrev.com/293382aa925f692808d148b593b91f0a97aba739/ui/display/manager/display_change_observer.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/72d5efb341c427ef0a91fc99d43a1f5a730e038e

commit 72d5efb341c427ef0a91fc99d43a1f5a730e038e
Author: Malay Keshav <malaykeshav@chromium.org>
Date: Wed Jun 13 18:56:45 2018

(merge) Add 2.0 DSF for external 4k display only if the display zoom is disabled

Display zoom is responsible for scaling when the flag is enabled so we
dont need to manualy set the device scale factor for external 4k
displays.

Bug:  851701 
Change-Id: I7b2789fa233dda89d3f2dd5031b5507c4c64b1ed
Component: Display Change Observer, 4k, Scaling
Reviewed-on: https://chromium-review.googlesource.com/1096343
Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#566541}(cherry picked from commit 293382aa925f692808d148b593b91f0a97aba739)
Reviewed-on: https://chromium-review.googlesource.com/1099615
Reviewed-by: Malay Keshav <malaykeshav@chromium.org>
Cr-Commit-Position: refs/branch-heads/3440@{#338}
Cr-Branched-From: 010ddcfda246975d194964ccf20038ebbdec6084-refs/heads/master@{#561733}
[modify] https://crrev.com/72d5efb341c427ef0a91fc99d43a1f5a730e038e/services/ui/display/screen_manager_ozone_internal_unittests.cc
[modify] https://crrev.com/72d5efb341c427ef0a91fc99d43a1f5a730e038e/ui/display/manager/display_change_observer.cc