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 e6ea05ea39c0b1e6e8c07c45f982b830b76ecd5a..c197ae7cafd4e45f5e11c44affee0c83ed46d734 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) {
 }