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`.

1 files changed, 0 insertions, 89 deletions

diff --git a/components/shared/gfx/print_tree.rs b/components/shared/gfx/print_tree.rs
deleted file mode 100644
index 03e47b21317..00000000000
--- a/components/shared/gfx/print_tree.rs
+++ /dev/null
@@ -1,89 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * 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/. */
-
-/// A struct that makes it easier to print out a pretty tree of data, which
-/// can be visually scanned more easily.
-pub struct PrintTree {
-    /// The current level of recursion.
-    level: u32,
-
-    /// An item which is queued up, so that we can determine if we need
-    /// a mid-tree prefix or a branch ending prefix.
-    queued_item: Option<String>,
-}
-
-impl PrintTree {
-    pub fn new(title: String) -> PrintTree {
-        println!("\u{250c} {}", title);
-        PrintTree {
-            level: 1,
-            queued_item: None,
-        }
-    }
-
-    /// Descend one level in the tree with the given title string.
-    pub fn new_level(&mut self, queued_title: String) {
-        self.flush_queued_item("\u{251C}\u{2500}");
-
-        self.print_level_prefix();
-
-        let items: Vec<&str> = queued_title.split('\n').collect();
-        println!("\u{251C}\u{2500} {}", items[0]);
-        for i in 1..items.len() {
-            self.print_level_child_indentation();
-            print!("{}", items[i]);
-            if i < items.len() {
-                println!();
-            }
-        }
-
-        self.level += 1;
-    }
-
-    /// Ascend one level in the tree.
-    pub fn end_level(&mut self) {
-        self.flush_queued_item("\u{2514}\u{2500}");
-        self.level -= 1;
-    }
-
-    /// Add an item to the current level in the tree.
-    pub fn add_item(&mut self, text: String) {
-        self.flush_queued_item("\u{251C}\u{2500}");
-        self.queued_item = Some(text);
-    }
-
-    fn print_level_prefix(&self) {
-        for _ in 0..self.level {
-            print!("\u{2502}  ");
-        }
-    }
-
-    fn print_level_child_indentation(&self) {
-        for _ in 0..(self.level + 1) {
-            print!("\u{2502}  ");
-        }
-        print!("{}", " ".repeat(7));
-    }
-
-    fn flush_queued_item(&mut self, prefix: &str) {
-        if let Some(queued_item) = self.queued_item.take() {
-            self.print_level_prefix();
-            let items: Vec<&str> = queued_item.split('\n').collect();
-            println!("{} {}", prefix, items[0]);
-            for i in 1..items.len() {
-                self.print_level_child_indentation();
-                print!("{}", items[i]);
-                if i < items.len() {
-                    println!();
-                }
-            }
-        }
-    }
-}
-
-impl Drop for PrintTree {
-    fn drop(&mut self) {
-        self.flush_queued_item("\u{2514}\u{2500}");
-    }
-}