Fixes a test dependency for building on non-aura snapshot_unittests

TEST=compile succeeds
BUG=244464

Review URL: https://chromiumcodereview.appspot.com/16164002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202667 0039d316-1c4b-4281-b951-d872f2087c98

ui/snapshot/snapshot.gyp

@@ -47,6 +47,7 @@
       'dependencies': [
         '../../skia/skia.gyp:skia',
         '../../base/base.gyp:base',
+        '../../base/base.gyp:test_support_base',
         '../../testing/gtest.gyp:gtest',
         '../ui.gyp:ui',
         'snapshot'