Gtk3 ui: Add libgtk3ui as a separate build component

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

Index: chrome/browser/ui/libgtk2ui/gtk2_ui.cc
diff --git a/chrome/browser/ui/libgtk2ui/gtk2_ui.cc b/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
index 23e63371bcb732a49b6032a57e99c7d32c50ce36..2f4f0535a274d58569b142b2c73fc02bfa50c3f3 100644
--- a/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
+++ b/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
@@ -21,7 +21,7 @@
 #include "base/stl_util.h"
 #include "base/strings/string_split.h"
 #include "base/strings/stringprintf.h"
-#include "chrome/browser/themes/theme_properties.h"
+#include "chrome/browser/themes/theme_properties.h"  // nogncheck

[Elliot Glaysher, 2016/10/25 21:48:57]

What's the nogncheck here for?

[Tom (Use chromium acct), 2016/10/25 22:00:23]

Without it, if I run gn gen --check, I get this error:

ERROR at //chrome/browser/ui/libgtk2ui/gtk2_ui.cc:24:11: Include not allowed.
#include "chrome/browser/themes/theme_properties.h"
          ^---------------------------------------
It is not in any dependency of
  //chrome/browser/ui/libgtk2ui:libgtk2ui
The include file is in the target(s):
  //chrome/browser:browser
which should somehow be reachable.


Might be related to the removal of allow_circular_includes_from in
chrome/browser/BUILD.gn

[Tom (Use chromium acct), 2016/10/25 22:41:46]

dpranke@:
Me and erg@ discussed this offline and we're not confident that nogncheck here
is the right solution.  I was hitting other problems when preserving
'allow_circular_includes_from'.

There's nothing we actually need to link against from theme_properties.h, it's
just a bunch of enums.  Maybe we can split the constants out?

[Dirk Pranke, 2016/10/25 23:56:10]

nogncheck is indeed the wrong solution :). 

It is subverting the intent and hiding a layering violation (i.e., you're not
actually fixing the circular
dependency). See the docs for `gn check` for more. The right thing to do is to
move theme_properties.h into a separate source_set() target that the libgtk2ui
targets depend on.

[Tom (Use chromium acct), 2016/10/26 18:20:01]

Done.

 #include "chrome/browser/ui/libgtk2ui/app_indicator_icon.h"
 #include "chrome/browser/ui/libgtk2ui/gtk2_event_loop.h"
 #include "chrome/browser/ui/libgtk2ui/gtk2_key_bindings_handler.h"