AnimationOptions: Include <memory> for std::unique_ptr

IWYU and stop relying on the header being included implicitly, which breaks
the libstdc++ build:

    In file included from ../../cc/trees/layer_tree_mutator.h:11:0,
                     from ../../cc/trees/layer_tree_mutator.cc:5:
    ../../cc/trees/animation_options.h:18:16: error: ‘unique_ptr’ in namespace ‘std’ does not name a template type
       virtual std::unique_ptr<AnimationOptions> Clone() const = 0;
                    ^~~~~~~~~~

Bug: 819294
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I876921fb915c41362f4674c30e46748688a78172
Reviewed-on: https://chromium-review.googlesource.com/1084597
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#564069}
1 file changed