Make the gyp files more cross-platform across the Unices

ui/ui.gyp

Index: ui/ui.gyp
diff --git a/ui/ui.gyp b/ui/ui.gyp
index 4e15b6c4361343938986e9a3ef3daed7d1612d6a..ac32a26a9217cc3229c876e1aa3658c3d825c86a 100644
--- a/ui/ui.gyp
+++ b/ui/ui.gyp
@@ -14,11 +14,13 @@
       ['exclude', '/(gtk|win|x11)_[^/]*\\.cc$'],
     ],
     'conditions': [
-      ['OS=="linux" or OS=="freebsd" or OS=="openbsd"', {'sources/': [
-        ['include', '/gtk/'],
-        ['include', '_(gtk|linux|posix|skia|x)\\.cc$'],
-        ['include', '/(gtk|x11)_[^/]*\\.cc$'],
-      ]}],
+      ['toolkit_uses_gtk==1', {
+        'sources/': [
+          ['include', '/gtk/'],
+          ['include', '_(gtk|linux|posix|skia|x)\\.cc$'],
+          ['include', '/(gtk|x11)_[^/]*\\.cc$'],
+        ],
+      }],
       ['OS=="mac"', {'sources/': [
         ['include', '/cocoa/'],
         ['include', '_(cocoa|mac|posix)\\.(cc|mm?)$'],