add gtk dep to test_support_common

R=erg@chromium.org
BUG=90442
TEST=test_support_common compiles w/ content shared lib.

Review URL: http://codereview.chromium.org/8429029

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@108156 0039d316-1c4b-4281-b951-d872f2087c98

content/content_tests.gypi

@@ -95,6 +95,13 @@
         '../webkit/quota/mock_special_storage_policy.cc',
         '../webkit/quota/mock_special_storage_policy.h',
       ],
+      'conditions': [
+        ['toolkit_uses_gtk == 1', {
+          'dependencies': [
+            '../build/linux/system.gyp:gtk',
+          ],
+        }],
+      ],
     },
     {
       'target_name': 'content_unittests',