Move kInvalidDisplayID to display_constants.h.

ui/display/types/display_constants.h

 // Copyright 2014 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.
 
 #ifndef UI_DISPLAY_TYPES_DISPLAY_CONSTANTS_H_
 #define UI_DISPLAY_TYPES_DISPLAY_CONSTANTS_H_
 
+#include <stdint.h>
+
+namespace display {
+
+// Display id that represents an invalid display. Often used as a default value
+// before display ids are known.

[Daniel Erat, 2016/11/21 17:33:57]

nit: s/id/ID/g in this comment

[kylechar, 2016/11/21 17:51:18]

Done.

+constexpr int64_t kInvalidDisplayID = -1;

[Daniel Erat, 2016/11/21 17:33:57]

it's a pretty big nit, but i think that "Id" is more common in constant names
than "ID":

% git grep 'const.*k[A-Z][a-zA-Z]*Id\b' | wc -l
3022
% git grep 'const.*k[A-Z][a-zA-Z]*ID\b' | wc -l
553

https://google.github.io/styleguide/cppguide.html#Function_Names touches on this
too: "Prefer to capitalize acronyms as single words (i.e. StartRpc(), not
StartRPC())." (a later sentence says that this also applies to constants.)

i realize that you're essentially just moving this out of a class, though, so
feel free to disregard this if it's a pain to update now. :-)

[kylechar, 2016/11/21 17:51:18]

I actually like kInvalidDisplayId better too. Changed.

+
+}  // namespace display
+
 namespace ui {
 
 // Used to describe the state of a multi-display configuration.
 enum MultipleDisplayState {

[sadrul, 2016/11/21 17:31:17]

We probably want to move these to display namespace too at some point.

[kylechar, 2016/11/21 17:51:18]

Totally agreed. There is a big chunk of ui/display/chromeos and ui/display/types
that needs to switch namespaces still.

   MULTIPLE_DISPLAY_STATE_INVALID,
   MULTIPLE_DISPLAY_STATE_HEADLESS,
   MULTIPLE_DISPLAY_STATE_SINGLE,
   MULTIPLE_DISPLAY_STATE_DUAL_MIRROR,
   MULTIPLE_DISPLAY_STATE_DUAL_EXTENDED,
   // TODO(oshima): consolidate DUAL_EXTENDED and MULTI_EXTENDED.
   MULTIPLE_DISPLAY_STATE_MULTI_EXTENDED,
 };
 
 // Video output types.
@@ skipping 34 matching lines @@
   COLOR_PROFILE_STANDARD,
   COLOR_PROFILE_DYNAMIC,
   COLOR_PROFILE_MOVIE,
   COLOR_PROFILE_READING,
   NUM_COLOR_PROFILES,
 };
 
 }  // namespace ui
 
 #endif  // UI_DISPLAY_TYPES_DISPLAY_CONSTANTS_H_