Move non-gfx things out of gfx_traits and create a base crate (#32296)

For a long time, `gfx_traits` has held a lot of things unrelated to graphics
and also unrelated to the `gfx` crate (which is mostly about fonts).
This is a cleanup which does a few things:

1. Move non `gfx` crate things out of `gfx_traits`. This is important in
   order to prevent dependency cycles with a different integration between
   layout, script, and fonts.
2. Rename the `msg` crate to `base`. It didn't really contain anything
   to do with messages and instead mostly holds ids, which are used
   across many different crates in Servo. This new crate will hold the
   *rare* data types that are widely used.

Details:

 - All BackgroundHangMonitor-related things from base to a new
   `background_hang_monitor_api` crate.
 - Moved `TraversalDirection` to `script_traits`
 - Moved `Epoch`-related things from `gfx_traits` to `base`.
 - Moved `PrintTree` to base. This should be widely useful in Servo.
 - Moved `WebrenderApi` from `base` to `webrender_traits` and renamed it
   to `WebRenderFontApi`.

components/layout_2020/Cargo.toml

@@ -15,6 +15,7 @@ doctest = false
 [dependencies]
 app_units = { workspace = true }
 atomic_refcell = { workspace = true }
+base = { workspace = true }
 canvas_traits = { workspace = true }
 bitflags = { workspace = true }
 cssparser = { workspace = true }
@@ -27,7 +28,6 @@ gfx_traits = { workspace = true }
 html5ever = { workspace = true }
 ipc-channel = { workspace = true }
 log = { workspace = true }
-msg = { workspace = true }
 net_traits = { workspace = true }
 parking_lot = { workspace = true }
 range = { path = "../range" }

components/layout_2020/context.rs

@@ -4,10 +4,10 @@
 
 use std::sync::{Arc, Mutex};
 
+use base::id::PipelineId;
 use fnv::FnvHashMap;
 use gfx::font_cache_thread::FontCacheThread;
 use gfx::font_context::FontContext;
-use msg::constellation_msg::PipelineId;
 use net_traits::image_cache::{
     ImageCache, ImageCacheResult, ImageOrMetadataAvailable, UsePlaceholder,
 };

components/layout_2020/display_list/mod.rs

@@ -5,12 +5,12 @@
 use std::cell::{OnceCell, RefCell};
 use std::sync::Arc;
 
+use base::id::BrowsingContextId;
+use base::WebRenderEpochToU16;
 use embedder_traits::Cursor;
 use euclid::{Point2D, SideOffsets2D, Size2D};
 use fnv::FnvHashMap;
 use gfx::text::glyph::GlyphStore;
-use gfx_traits::WebRenderEpochToU16;
-use msg::constellation_msg::BrowsingContextId;
 use net_traits::image_cache::UsePlaceholder;
 use script_traits::compositor::{CompositorDisplayListInfo, ScrollSensitivity, ScrollTreeNodeId};
 use servo_geometry::MaxRect;

components/layout_2020/display_list/stacking_context.rs

@@ -5,9 +5,9 @@
 use std::cell::RefCell;
 use std::mem;
 
+use base::print_tree::PrintTree;
 use euclid::default::Rect;
 use euclid::SideOffsets2D;
-use gfx_traits::print_tree::PrintTree;
 use log::warn;
 use script_traits::compositor::{ScrollSensitivity, ScrollTreeNodeId, ScrollableNodeInfo};
 use servo_arc::Arc as ServoArc;

components/layout_2020/dom.rs

@@ -6,8 +6,8 @@ use std::marker::PhantomData;
 use std::sync::{Arc, Mutex};
 
 use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
+use base::id::{BrowsingContextId, PipelineId};
 use html5ever::{local_name, namespace_url, ns};
-use msg::constellation_msg::{BrowsingContextId, PipelineId};
 use net_traits::image::base::Image as NetImage;
 use script_layout_interface::wrapper_traits::{
     LayoutDataTrait, LayoutNode, ThreadSafeLayoutElement, ThreadSafeLayoutNode,

components/layout_2020/fragment_tree/base_fragment.rs

@@ -3,7 +3,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 use bitflags::bitflags;
-use gfx_traits::{combine_id_with_fragment_type, FragmentType};
+use script_layout_interface::{combine_id_with_fragment_type, FragmentType};
 use serde::Serialize;
 use style::dom::OpaqueNode;
 use style::selector_parser::PseudoElement;

components/layout_2020/fragment_tree/box_fragment.rs

@@ -3,7 +3,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 use app_units::Au;
-use gfx_traits::print_tree::PrintTree;
+use base::print_tree::PrintTree;
 use serde::Serialize;
 use servo_arc::Arc as ServoArc;
 use style::computed_values::overflow_x::T as ComputedOverflow;

components/layout_2020/fragment_tree/fragment.rs

@@ -5,10 +5,10 @@
 use std::sync::Arc;
 
 use app_units::Au;
+use base::id::{BrowsingContextId, PipelineId};
+use base::print_tree::PrintTree;
 use gfx::font::FontMetrics;
 use gfx::text::glyph::GlyphStore;
-use gfx_traits::print_tree::PrintTree;
-use msg::constellation_msg::{BrowsingContextId, PipelineId};
 use serde::Serialize;
 use servo_arc::Arc as ServoArc;
 use style::properties::ComputedValues;

components/layout_2020/fragment_tree/fragment_tree.rs

@@ -3,9 +3,9 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 use app_units::Au;
+use base::print_tree::PrintTree;
 use euclid::default::{Point2D, Rect, Size2D};
 use fxhash::FxHashSet;
-use gfx_traits::print_tree::PrintTree;
 use script_traits::compositor::ScrollSensitivity;
 use serde::Serialize;
 use style::animation::AnimationSetKey;

components/layout_2020/fragment_tree/positioning_fragment.rs

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use gfx_traits::print_tree::PrintTree;
+use base::print_tree::PrintTree;
 use serde::Serialize;
 use servo_arc::Arc as ServoArc;
 use style::logical_geometry::WritingMode;

components/layout_2020/replaced.rs

@@ -6,10 +6,10 @@ use std::fmt;
 use std::sync::{Arc, Mutex};
 
 use app_units::Au;
+use base::id::{BrowsingContextId, PipelineId};
 use canvas_traits::canvas::{CanvasId, CanvasMsg, FromLayoutMsg};
 use data_url::DataUrl;
 use ipc_channel::ipc::{self, IpcSender};
-use msg::constellation_msg::{BrowsingContextId, PipelineId};
 use net_traits::image::base::Image;
 use net_traits::image_cache::{ImageOrMetadataAvailable, UsePlaceholder};
 use serde::Serialize;