Revert "kUseMonitorColorSpace: mark DISABLED_BY_DEFAULT"

This reverts commit 51b5b7bc.

Reason for revert: This CL landed on master so that it could be 
cherry-picked on M66 branch, which it did on crrev.com/c/1013755,
so it can be reverted now.

Original change's description:
> kUseMonitorColorSpace: mark DISABLED_BY_DEFAULT
> 
> Mark kUseMonitorColorSpace disabled by default to avoid
> the blue-color-looks-purple problems detailed in the bug.
> This is just a temporary CL to allow cherry-picking it
> into the beta branch.
> 
> TBR=dcastagna@chromium.org
> 
> Bug: 809909
> Change-Id: I35bb8cc48c26091cb1752d3d7709a48d23fb4c6e
> Reviewed-on: https://chromium-review.googlesource.com/1012305
> Reviewed-by: Miguel Casas <mcasas@chromium.org>
> Commit-Queue: Miguel Casas <mcasas@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#551152}

TBR=mcasas@chromium.org

Change-Id: Ie1f6d2eae27e1332374f696a5d17a8dacebac3e6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 809909
Reviewed-on: https://chromium-review.googlesource.com/1015142Reviewed-by: Miguel Casas <mcasas@chromium.org>
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551406}

ui/display/display_switches.cc

@@ -68,7 +68,7 @@ const base::Feature kHighDynamicRange{"HighDynamicRange",
 // Enables using the monitor's provided color space information when rendering.
 // TODO(mcasas): remove this flag http://crbug.com/771345.
 const base::Feature kUseMonitorColorSpace{"UseMonitorColorSpace",
-                                          base::FEATURE_DISABLED_BY_DEFAULT};
+                                          base::FEATURE_ENABLED_BY_DEFAULT};
 #endif
 
 }  // namespace features