cc: Move SyncedScrollOffset to scroll tree

cc/trees/layer_tree_host_common_unittest.cc

Index: cc/trees/layer_tree_host_common_unittest.cc
diff --git a/cc/trees/layer_tree_host_common_unittest.cc b/cc/trees/layer_tree_host_common_unittest.cc
index cfcc1ec122abbb118198965e723fe2a79e3717b6..3c6ab8f4e252576605cc6479297c93fe52536cdc 100644
--- a/cc/trees/layer_tree_host_common_unittest.cc
+++ b/cc/trees/layer_tree_host_common_unittest.cc
@@ -10067,7 +10067,8 @@ TEST_F(LayerTreeHostCommonTest, ScrollTreeBuilderTest) {
 
   // Property tree root
   ScrollTree scroll_tree = host()->property_trees()->scroll_tree;
-  ScrollTree expected_scroll_tree;
+  PropertyTrees property_trees;
+  ScrollTree expected_scroll_tree = property_trees.scroll_tree;
   ScrollNode* property_tree_root = expected_scroll_tree.Node(0);
   property_tree_root->id = kRootPropertyTreeNodeId;
   property_tree_root->parent_id = kInvalidPropertyTreeNodeId;
@@ -10150,6 +10151,12 @@ TEST_F(LayerTreeHostCommonTest, ScrollTreeBuilderTest) {
   scroll_parent5.data.transform_id = parent5->transform_tree_index();
   expected_scroll_tree.Insert(scroll_parent5, 1);
 
+  expected_scroll_tree.synced_scroll_offset(parent2->id())
+      ->PushFromMainThread(gfx::ScrollOffset(0, 0));
+  expected_scroll_tree.synced_scroll_offset(child7->id())
+      ->PushFromMainThread(gfx::ScrollOffset(0, 0));
+  expected_scroll_tree.synced_scroll_offset(grand_child11->id())
+      ->PushFromMainThread(gfx::ScrollOffset(0, 0));
   expected_scroll_tree.set_needs_update(false);
 
   EXPECT_EQ(expected_scroll_tree, scroll_tree);