Implement basic Time To First Paint and First Contentful Paint PWMs

components/script_layout_interface/message.rs

@@ -7,6 +7,7 @@ use app_units::Au;
 use euclid::{Point2D, Rect};
 use gfx_traits::Epoch;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
+use metrics::PaintTimeMetrics;
 use msg::constellation_msg::PipelineId;
 use net_traits::image_cache::ImageCache;
 use profile_traits::mem::ReportsChan;
@@ -89,6 +90,9 @@ pub enum Msg {
 
     /// Tells layout that script has added some paint worklet modules.
     RegisterPaint(Atom, Vec<Atom>, Arc<Painter>),
+
+    /// Send to layout the precise time when the navigation started.
+    SetNavigationStart(f64),
 }
 
 
@@ -158,4 +162,5 @@ pub struct NewLayoutThreadInfo {
     pub image_cache: Arc<ImageCache>,
     pub content_process_shutdown_chan: Option<IpcSender<()>>,
     pub layout_threads: usize,
+    pub paint_time_metrics: PaintTimeMetrics,
 }