Add serialization/deserialization for FakePictureLayer for testing.

cc/trees/layer_tree_host_unittest.cc

Index: cc/trees/layer_tree_host_unittest.cc
diff --git a/cc/trees/layer_tree_host_unittest.cc b/cc/trees/layer_tree_host_unittest.cc
index cf25b1cfe644b2e479d3f31ccbaa81fec7630243..e0eb2f064bc5c49828a8d4389170ed978ea50733 100644
--- a/cc/trees/layer_tree_host_unittest.cc
+++ b/cc/trees/layer_tree_host_unittest.cc
@@ -287,10 +287,7 @@ class LayerTreeHostTestReadyToActivateNonEmpty
 
 // No single thread test because the commit goes directly to the active tree in
 // single thread mode, so notify ready to activate is skipped.
-// No remote test because we currently don't deserialize FakePictureLayer,
-// so on the impl side, PictureLayerImpl is created instead of
-// FakePictureLayerImpl, see crbug/657871.
-MULTI_THREAD_TEST_F(LayerTreeHostTestReadyToActivateNonEmpty);
+REMOTE_AND_MULTI_THREAD_TEST_F(LayerTreeHostTestReadyToActivateNonEmpty);
 
 // Test if the LTHI receives ReadyToDraw notifications from the TileManager when
 // no raster tasks get scheduled.