Remove more IPC messages between script and layout (#32377)

Instead of bouncing messages from the compositor to script and then to
layout, just have script call methods on Layout. Additionally, we do not
need to send any followup messages to script for these messages. Instead
just execute code after calling the method on Layout.

components/script/script_thread.rs

@@ -26,8 +26,8 @@ use std::rc::Rc;
 use std::result::Result;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
+use std::thread;
 use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
-use std::{ptr, thread};
 
 use background_hang_monitor_api::{
     BackgroundHangMonitor, BackgroundHangMonitorExitSignal, HangAnnotation, MonitoredComponentId,
@@ -36,6 +36,7 @@ use background_hang_monitor_api::{
 use base::id::{
     BrowsingContextId, HistoryStateId, PipelineId, PipelineNamespace, TopLevelBrowsingContextId,
 };
+use base::Epoch;
 use bluetooth_traits::BluetoothRequest;
 use canvas_traits::webgl::WebGLPipeline;
 use chrono::{DateTime, Local};
@@ -46,7 +47,6 @@ use devtools_traits::{
 };
 use embedder_traits::EmbedderMsg;
 use euclid::default::{Point2D, Rect};
-use euclid::Vector2D;
 use gfx::font_cache_thread::FontCacheThread;
 use headers::{HeaderMapExt, LastModified, ReferrerPolicy as ReferrerPolicyHeader};
 use html5ever::{local_name, namespace_url, ns};
@@ -73,13 +73,15 @@ use parking_lot::Mutex;
 use percent_encoding::percent_decode;
 use profile_traits::mem::{self as profile_mem, OpaqueSender, ReportsChan};
 use profile_traits::time::{self as profile_time, profile, ProfilerCategory};
-use script_layout_interface::{LayoutConfig, LayoutFactory, ReflowGoal, ScriptThreadFactory};
+use script_layout_interface::{
+    node_id_from_scroll_id, LayoutConfig, LayoutFactory, ReflowGoal, ScriptThreadFactory,
+};
 use script_traits::webdriver_msg::WebDriverScriptCommand;
 use script_traits::{
     CompositorEvent, ConstellationControlMsg, DiscardBrowsingContext, DocumentActivity,
-    EventResult, HistoryEntryReplacement, InitialScriptState, JsEvalResult, LayoutControlMsg,
-    LayoutMsg, LoadData, LoadOrigin, MediaSessionActionType, MouseButton, MouseEventType,
-    NewLayoutInfo, Painter, ProgressiveWebMetricType, ScriptMsg, ScriptToConstellationChan,
+    EventResult, HistoryEntryReplacement, InitialScriptState, JsEvalResult, LayoutMsg, LoadData,
+    LoadOrigin, MediaSessionActionType, MouseButton, MouseEventType, NewLayoutInfo, Painter,
+    ProgressiveWebMetricType, ScriptMsg, ScriptToConstellationChan, ScrollState,
     StructuredSerializedData, TimerSchedulerMsg, TouchEventType, TouchId, UntrustedNodeAddress,
     UpdatePipelineIdReason, WheelDelta, WindowSizeData, WindowSizeType,
 };
@@ -91,7 +93,6 @@ use style::thread_state::{self, ThreadState};
 use time::precise_time_ns;
 use url::Position;
 use webgpu::WebGPUMsg;
-use webrender_api::units::LayoutPixel;
 use webrender_api::DocumentId;
 use webrender_traits::WebRenderScriptApi;
 
@@ -1836,11 +1837,6 @@ impl ScriptThread {
                     .profile_event(ScriptThreadEventCategory::SetViewport, Some(id), || {
                         self.handle_viewport(id, rect);
                     }),
-                FromConstellation(ConstellationControlMsg::SetScrollState(id, scroll_state)) => {
-                    self.profile_event(ScriptThreadEventCategory::SetScrollState, Some(id), || {
-                        self.handle_set_scroll_state(id, &scroll_state);
-                    })
-                },
                 FromConstellation(ConstellationControlMsg::TickAllAnimations(
                     pipeline_id,
                     tick_type,
@@ -2097,7 +2093,6 @@ impl ScriptThread {
                 ExitScriptThread => None,
                 SendEvent(id, ..) => Some(id),
                 Viewport(id, ..) => Some(id),
-                SetScrollState(id, ..) => Some(id),
                 GetTitle(id) => Some(id),
                 SetDocumentActivity(id, ..) => Some(id),
                 SetThrottled(id, ..) => Some(id),
@@ -2123,7 +2118,8 @@ impl ScriptThread {
                 ExitFullScreen(id, ..) => Some(id),
                 MediaSessionAction(..) => None,
                 SetWebGPUPort(..) => None,
-                ForLayoutFromConstellation(_, id) => Some(id),
+                SetScrollStates(id, ..) => Some(id),
+                SetEpochPaintTime(id, ..) => Some(id),
             },
             MixedMessage::FromDevtools(_) => None,
             MixedMessage::FromScript(ref inner_msg) => match *inner_msg {
@@ -2348,7 +2344,6 @@ impl ScriptThread {
             },
             msg @ ConstellationControlMsg::AttachLayout(..) |
             msg @ ConstellationControlMsg::Viewport(..) |
-            msg @ ConstellationControlMsg::SetScrollState(..) |
             msg @ ConstellationControlMsg::Resize(..) |
             msg @ ConstellationControlMsg::ExitFullScreen(..) |
             msg @ ConstellationControlMsg::SendEvent(..) |
@@ -2356,22 +2351,53 @@ impl ScriptThread {
             msg @ ConstellationControlMsg::ExitScriptThread => {
                 panic!("should have handled {:?} already", msg)
             },
-            ConstellationControlMsg::ForLayoutFromConstellation(msg, pipeline_id) => {
-                self.handle_layout_message_from_constellation(msg, pipeline_id)
+            ConstellationControlMsg::SetScrollStates(pipeline_id, scroll_states) => {
+                self.handle_set_scroll_states_msg(pipeline_id, scroll_states)
+            },
+            ConstellationControlMsg::SetEpochPaintTime(pipeline_id, epoch, time) => {
+                self.handle_set_epoch_paint_time(pipeline_id, epoch, time)
             },
         }
     }
 
-    fn handle_layout_message_from_constellation(
+    fn handle_set_scroll_states_msg(
         &self,
-        msg: LayoutControlMsg,
         pipeline_id: PipelineId,
+        scroll_states: Vec<ScrollState>,
     ) {
         let Some(window) = self.documents.borrow().find_window(pipeline_id) else {
-            warn!("Received layout message pipeline {pipeline_id} closed: {msg:?}.");
+            warn!("Received scroll states for closed pipeline {pipeline_id}");
             return;
         };
-        window.layout_mut().handle_constellation_message(msg);
+
+        self.profile_event(
+            ScriptThreadEventCategory::SetScrollState,
+            Some(pipeline_id),
+            || {
+                window.layout_mut().set_scroll_states(&scroll_states);
+
+                let mut scroll_offsets = HashMap::new();
+                for scroll_state in scroll_states.into_iter() {
+                    let scroll_offset = scroll_state.scroll_offset;
+                    if scroll_state.scroll_id.is_root() {
+                        window.update_viewport_for_scroll(-scroll_offset.x, -scroll_offset.y);
+                    } else if let Some(node_id) =
+                        node_id_from_scroll_id(scroll_state.scroll_id.0 as usize)
+                    {
+                        scroll_offsets.insert(OpaqueNode(node_id), -scroll_offset);
+                    }
+                }
+                window.set_scroll_offsets(scroll_offsets)
+            },
+        )
+    }
+
+    fn handle_set_epoch_paint_time(&self, pipeline_id: PipelineId, epoch: Epoch, time: u64) {
+        let Some(window) = self.documents.borrow().find_window(pipeline_id) else {
+            warn!("Received set epoch paint time message for closed pipeline {pipeline_id}.");
+            return;
+        };
+        window.layout_mut().set_epoch_paint_time(epoch, time);
     }
 
     fn handle_msg_from_webgpu_server(&self, msg: WebGPUMsg) {
@@ -2763,32 +2789,6 @@ impl ScriptThread {
         warn!("Page rect message sent to nonexistent pipeline");
     }
 
-    fn handle_set_scroll_state(
-        &self,
-        id: PipelineId,
-        scroll_states: &[(UntrustedNodeAddress, Vector2D<f32, LayoutPixel>)],
-    ) {
-        let window = match self.documents.borrow().find_window(id) {
-            Some(window) => window,
-            None => {
-                return warn!(
-                    "Set scroll state message sent to nonexistent pipeline: {:?}",
-                    id
-                );
-            },
-        };
-
-        let mut scroll_offsets = HashMap::new();
-        for &(node_address, ref scroll_offset) in scroll_states {
-            if node_address == UntrustedNodeAddress(ptr::null()) {
-                window.update_viewport_for_scroll(-scroll_offset.x, -scroll_offset.y);
-            } else {
-                scroll_offsets.insert(OpaqueNode(node_address.0 as usize), -*scroll_offset);
-            }
-        }
-        window.set_scroll_offsets(scroll_offsets)
-    }
-
     fn handle_new_layout(&self, new_layout_info: NewLayoutInfo, origin: MutableOrigin) {
         let NewLayoutInfo {
             parent_info,