aura: Make 'ui' buildable without gtk.

build/linux/system.gyp

Index: build/linux/system.gyp
diff --git a/build/linux/system.gyp b/build/linux/system.gyp
index 688903fbe0213241fe32eaa1ca12fc10f17643dc..81b619edb764dfe7bc88207edf2080a54cc89add 100644
--- a/build/linux/system.gyp
+++ b/build/linux/system.gyp
@@ -507,6 +507,42 @@
       ],
     },
     {
+      'target_name': 'pangocairo',
+      'type': 'settings',
+      'toolsets': ['host', 'target'],
+      'conditions': [
+        ['_toolset=="target"', {
+          'direct_dependent_settings': {
+            'cflags': [
+              '<!@(<(pkg-config) --cflags pangocairo)',
+            ],
+          },
+          'link_settings': {
+            'ldflags': [
+              '<!@(<(pkg-config) --libs-only-L --libs-only-other pangocairo)',
+            ],
+            'libraries': [
+              '<!@(<(pkg-config) --libs-only-l pangocairo)',
+            ],
+          },
+        }, {
+          'direct_dependent_settings': {
+            'cflags': [
+              '<!@(pkg-config --cflags pangocairo)',
+            ],
+          },
+          'link_settings': {
+            'ldflags': [
+              '<!@(pkg-config --libs-only-L --libs-only-other pangocairo)',
+            ],
+            'libraries': [
+              '<!@(pkg-config --libs-only-l pangocairo)',
+            ],
+          },
+        }],
+      ],
+    },
+    {
       'target_name': 'libresolv',
       'type': 'settings',
       'link_settings': {