CC Animations: Fix the case when main-thread player changes layer_id.

cc/test/animation_timelines_test_common.cc

Index: cc/test/animation_timelines_test_common.cc
diff --git a/cc/test/animation_timelines_test_common.cc b/cc/test/animation_timelines_test_common.cc
index 9212da6169b60db6a3390949d23133bdbac22247..6df5bd18ea56bc5e1e6f1dc0c1d91585e33835b9 100644
--- a/cc/test/animation_timelines_test_common.cc
+++ b/cc/test/animation_timelines_test_common.cc
@@ -197,9 +197,11 @@ AnimationTimelinesTest::AnimationTimelinesTest()
       host_impl_(nullptr),
       timeline_id_(AnimationIdProvider::NextTimelineId()),
       player_id_(AnimationIdProvider::NextPlayerId()),
-      layer_id_(1) {
+      next_test_layer_id_(0) {
   host_ = client_.host();
   host_impl_ = client_impl_.host();
+
+  layer_id_ = NextTestLayerId();
 }
 
 AnimationTimelinesTest::~AnimationTimelinesTest() {
@@ -258,4 +260,9 @@ AnimationPlayer* AnimationTimelinesTest::GetImplPlayerForLayerId(int layer_id) {
                             : nullptr;
 }
 
+int AnimationTimelinesTest::NextTestLayerId() {
+  next_test_layer_id_++;
+  return next_test_layer_id_;
+}
+
 }  // namespace cc