Minimize black screen during the boot with multi displays

ash/ash_constants.h

Index: ash/ash_constants.h
diff --git a/ash/ash_constants.h b/ash/ash_constants.h
index 7b8d3f7b348425766f25e89f1ff360ada87d16cb..8e889851ea668db4fe70d0c74dac9fd7dba34aae 100644
--- a/ash/ash_constants.h
+++ b/ash/ash_constants.h
@@ -30,6 +30,11 @@ ASH_EXPORT extern const int kResizeOutsideBoundsSize;
 ASH_EXPORT extern const int kResizeOutsideBoundsScaleForTouch;
 ASH_EXPORT extern const int kResizeInsideBoundsSize;
 
+#if defined(OS_CHROMEOS)
+// Background color used for the Chrome OS boot splash screen.
+extern const SkColor kChromeOsBootColor;
+#endif
+
 // The border color of keyboard focus for launcher items and system tray.
 extern const SkColor kFocusBorderColor;