Replace unique_ptr.reset(other_unique_ptr.release()) with std::move() in cc/trees/

BUG=644626

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2745963002
Cr-Commit-Position: refs/heads/master@{#456375}
diff --git a/cc/trees/layer_tree_host_common_unittest.cc b/cc/trees/layer_tree_host_common_unittest.cc
index 4f4511d9..ed9c242b 100644
--- a/cc/trees/layer_tree_host_common_unittest.cc
+++ b/cc/trees/layer_tree_host_common_unittest.cc
@@ -5728,7 +5728,7 @@
   clip_child->test_properties()->clip_parent = clip_parent;
   std::unique_ptr<std::set<LayerImpl*>> clip_children(new std::set<LayerImpl*>);
   clip_children->insert(clip_child);
-  clip_parent->test_properties()->clip_children.reset(clip_children.release());
+  clip_parent->test_properties()->clip_children = std::move(clip_children);
 
   intervening->SetMasksToBounds(true);
   clip_parent->SetMasksToBounds(true);