Add GDK_DISABLE=color-mgmt

This flag is meant to turn off color management features of GDK.
If this is set, all surfaces will report sRGB as their preferred
color state.

docs/reference/gtk/running.md

@@ -358,6 +358,9 @@ disable certain features.
 `offload`
 : Disable graphics offload to subsurfaces
 
+`color-mgmt`
+: Disable color management
+
 ### `GDK_GL_DISABLE`
 
 This variable can be set to a list of values, which cause GDK to

gdk/gdk.c

@@ -151,6 +151,7 @@ static const GdkDebugKey gdk_feature_keys[] = {
   { "vulkan",     GDK_FEATURE_VULKAN,           "Disable Vulkan support" },
   { "dmabuf",     GDK_FEATURE_DMABUF,           "Disable dmabuf support" },
   { "offload",    GDK_FEATURE_OFFLOAD,          "Disable graphics offload" },
+  { "color-mgmt", GDK_FEATURE_COLOR_MANAGEMENT, "Disable color management" },
 };
 
 

gdk/gdkdebugprivate.h

@@ -63,9 +63,10 @@ typedef enum {
   GDK_FEATURE_VULKAN           = 1 << 6,
   GDK_FEATURE_DMABUF           = 1 << 7,
   GDK_FEATURE_OFFLOAD          = 1 << 8,
+  GDK_FEATURE_COLOR_MANAGEMENT = 1 << 9,
 } GdkFeatures;
 
-#define GDK_ALL_FEATURES ((1 << 9) - 1)
+#define GDK_ALL_FEATURES ((1 << 10) - 1)
 
 extern guint _gdk_debug_flags;