cc: Fix readback from non-root layers.

cc/cc_tests.gyp

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'chromium_code': 1,
     'cc_unit_tests_source_files': [
       'animation/animation_unittest.cc',
       'animation/keyframed_animation_curve_unittest.cc',
@@ skipping 53 matching lines @@
       'scheduler/texture_uploader_unittest.cc',
       'scheduler/vsync_time_source_unittest.cc',
       'test/fake_web_graphics_context_3d_unittest.cc',
       'trees/damage_tracker_unittest.cc',
       'trees/layer_sorter_unittest.cc',
       'trees/layer_tree_host_common_unittest.cc',
       'trees/layer_tree_host_impl_unittest.cc',
       'trees/layer_tree_host_pixeltest_filters.cc',
       'trees/layer_tree_host_pixeltest_masks.cc',
       'trees/layer_tree_host_pixeltest_on_demand_raster.cc',
+      'trees/layer_tree_host_pixeltest_readback.cc',
       'trees/layer_tree_host_unittest_animation.cc',
       'trees/layer_tree_host_unittest.cc',
       'trees/layer_tree_host_unittest_context.cc',
       'trees/layer_tree_host_unittest_damage.cc',
       'trees/layer_tree_host_unittest_delegated.cc',
       'trees/layer_tree_host_unittest_occlusion.cc',
       'trees/layer_tree_host_unittest_scroll.cc',
       'trees/layer_tree_host_unittest_video.cc',
       'trees/occlusion_tracker_unittest.cc',
       'trees/quad_culler_unittest.cc',
@@ skipping 221 matching lines @@
           'variables': {
             'test_suite_name': 'cc_perftests',
             'input_shlib_path': '<(SHARED_LIB_DIR)/<(SHARED_LIB_PREFIX)cc_perftests<(SHARED_LIB_SUFFIX)',
           },
           'includes': [ '../build/apk_test.gypi' ],
         },
       ],
     }]
   ],
 }