Allow setting userscripts directly without the need of files (#35388)

* Allow settings userscripts through preferences

Signed-off-by: Tony <legendmastertony@gmail.com>

* mach fmt instead of cargo fmt

Signed-off-by: Tony <legendmastertony@gmail.com>

* Fix pref loading not working for array values

Signed-off-by: Tony <legendmastertony@gmail.com>

* Use pref! in userscripts instead

Signed-off-by: Tony <legendmastertony@gmail.com>

* Implement the model jdm suggested
- Remove userscripts from all places and move it to servoshell
- Add in `UserContentManager` struct and passing it through `Servo::new`
all the way down to script thread

Signed-off-by: Tony <legendmastertony@gmail.com>

* Apply suggestions from code review and format

Signed-off-by: Tony <legendmastertony@gmail.com>

* Revert unrelated change

Signed-off-by: Tony <legendmastertony@gmail.com>

---------

Signed-off-by: Tony <legendmastertony@gmail.com>
Signed-off-by: Tony <68118705+Legend-Master@users.noreply.github.com>

components/shared/embedder/lib.rs

@@ -10,6 +10,7 @@
 
 pub mod input_events;
 pub mod resources;
+pub mod user_content_manager;
 mod webdriver;
 
 use std::fmt::{Debug, Error, Formatter};

components/shared/embedder/user_content_manager.rs

@@ -0,0 +1,55 @@
+/* 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/. */
+
+use std::path::PathBuf;
+
+use malloc_size_of::MallocSizeOfOps;
+use malloc_size_of_derive::MallocSizeOf;
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Debug, Default, Deserialize, MallocSizeOf, Serialize)]
+pub struct UserContentManager {
+    user_scripts: Vec<UserScript>,
+}
+
+impl UserContentManager {
+    pub fn new() -> Self {
+        UserContentManager::default()
+    }
+
+    pub fn add_script(&mut self, script: impl Into<UserScript>) {
+        self.user_scripts.push(script.into());
+    }
+
+    pub fn scripts(&self) -> &[UserScript] {
+        &self.user_scripts
+    }
+}
+
+#[derive(Clone, Debug, Deserialize, Serialize)]
+pub struct UserScript {
+    pub script: String,
+    pub source_file: Option<PathBuf>,
+}
+
+// Maybe we should implement `MallocSizeOf` for `PathBuf` in `malloc_size_of` crate?
+impl malloc_size_of::MallocSizeOf for UserScript {
+    fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
+        let mut sum = 0;
+        sum += self.script.size_of(ops);
+        if let Some(path) = &self.source_file {
+            sum += unsafe { ops.malloc_size_of(path.as_path()) };
+        }
+        sum
+    }
+}
+
+impl<T: Into<String>> From<T> for UserScript {
+    fn from(script: T) -> Self {
+        UserScript {
+            script: script.into(),
+            source_file: None,
+        }
+    }
+}