Add simplistic HLG->SDR conversion.

ui/gfx/color_transform.cc

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/color_transform.h"
 
 #include <vector>
 
 #include "base/logging.h"
 #include "ui/gfx/color_space.h"
@@ skipping 556 matching lines @@
           // See SMPTE 1886
           from_.transfer_ = ColorSpace::TransferID::GAMMA24;
           break;
 
         case ColorSpace::TransferID::SMPTEST2084:
           // We don't have an HDR display, so replace SMPTE 2084 with something
           // that returns ranges more or less suitable for a normal display.
           from_.transfer_ = ColorSpace::TransferID::SMPTEST2084_NON_HDR;
           break;
 
+        case ColorSpace::TransferID::ARIB_STD_B67:
+          // Interpreting HLG using a gamma 2.4 works reasonably well for SDR
+          // displays. Once we have HDR output capabilies, we'll need to
+          // change this.
+          from_.transfer_ = ColorSpace::TransferID::GAMMA24;
+          break;
+
         default:  // Do nothing
           break;
       }
 
       // TODO(hubbe): shrink gamuts here (never stretch gamuts)
     }
 
     Transform* from_transfer_matrix =
         from_.matrix_ == ColorSpace::MatrixID::BT2020_CL ? &b_ : &a_;
     Transform* to_transfer_matrix =
@@ skipping 141 matching lines @@
           std::unique_ptr<ColorTransform>(
               new QCMSColorTransform(GetXYZD50Profile(), to_profile))));
     } else {
       return std::unique_ptr<ColorTransform>(
           new ColorSpaceToColorSpaceTransform(from, to, intent));
     }
   }
 }
 
 }  // namespace gfx