cc/blimp: Add synchronization for scroll/scale state.

cc/trees/layer_tree_host_common.cc

Index: cc/trees/layer_tree_host_common.cc
diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index 7f0bf2500360f358be9389dd7c76b20ff61463c9..3bfe11233610978fb1736b5550f540cf05f20abe 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -184,6 +184,10 @@ void LayerTreeHostCommon::ScrollUpdateInfo::FromProtobuf(
   scroll_delta = ProtoToVector2d(proto.scroll_delta());
 }
 
+ReflectedMainFrameState::ReflectedMainFrameState() : page_scale_delta(1.0f) {}
+
+ReflectedMainFrameState::~ReflectedMainFrameState() = default;
+
 ScrollAndScaleSet::ScrollAndScaleSet()
     : page_scale_delta(1.f), top_controls_delta(0.f) {
 }