Rename animation_unittest.cc to keyframe_model_unittest.cc

In patch https://chromium-review.googlesource.com/906830 we renamed cc
side animation related classes but it missed a test file listed in the
subject. It should be fixed prior to next renaming patch.

Bug: 807667
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: Ib8c86a9f28b12b6a298f5d284c7ceb7171db1958
Reviewed-on: https://chromium-review.googlesource.com/924172
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537377}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index cefc5a9..9d81997 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -704,8 +704,8 @@
     "animation/animation_host_unittest.cc",
     "animation/animation_player_unittest.cc",
     "animation/animation_timeline_unittest.cc",
-    "animation/animation_unittest.cc",
     "animation/element_animations_unittest.cc",
+    "animation/keyframe_model_unittest.cc",
     "animation/keyframed_animation_curve_unittest.cc",
     "animation/scroll_offset_animation_curve_unittest.cc",
     "animation/scroll_timeline_unittest.cc",