aura: Make 'ui' buildable without gtk.

ui/ui_unittests.gypi

Index: ui/ui_unittests.gypi
diff --git a/ui/ui_unittests.gypi b/ui/ui_unittests.gypi
index b6fa721dd4e6c0bde9b277720d3e34eb399b84ef..1f2ea7ff062bc6875e0a95d9449e6c252829d82f 100644
--- a/ui/ui_unittests.gypi
+++ b/ui/ui_unittests.gypi
@@ -138,12 +138,9 @@
             'gfx/interpolated_transform_unittest.cc',
           ],
         }],
-        ['toolkit_uses_gtk == 1', {
-          'sources': [
-            'base/dragdrop/gtk_dnd_util_unittest.cc',
-          ],
+        ['use_glib == 1', {
           'dependencies': [
-            '../build/linux/system.gyp:gtk',
+            '../build/linux/system.gyp:pangocairo',
             '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
             'base/strings/ui_strings.gyp:ui_unittest_strings',
           ],
@@ -160,6 +157,14 @@
             }],
           ],
         }],
+        ['toolkit_uses_gtk == 1', {
+          'sources': [
+            'base/dragdrop/gtk_dnd_util_unittest.cc',
+          ],
+          'dependencies': [
+            '../build/linux/system.gyp:gtk',
+          ],
+        }],
         ['toolkit_views==1', {
           'sources': [
             'gfx/render_text_unittest.cc',