indexeddb: Support enabling IndexedDB after startup (#39177)

The servodriver harness requires preference-gated web platform features
to be toggleable at any point in the browsing session's lifetime, rather
than at startup. To support toggling IndexedDB, we need to ensure the
IDB manager thread is always started.

Testing: Verified when running `./mach test-wpt /IndexedDB --headless
--product servodriver`. We don't run servodriver in CI yet.
Fixes: #39175

---------

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

components/net/indexeddb/idb_thread.rs

@@ -224,9 +224,6 @@ impl IndexedDBManager {
 
 impl IndexedDBManager {
     fn start(&mut self) {
-        if !pref!(dom_indexeddb_enabled) {
-            return;
-        }
         loop {
             // FIXME:(arihant2math) No message *most likely* means that
             // the ipc sender has been dropped, so we break the look

components/script/dom/idbfactory.rs

@@ -58,7 +58,9 @@ impl IDBFactoryMethods<crate::DomTypeHolder> for IDBFactory {
         let request = IDBOpenDBRequest::new(&self.global(), CanGc::note());
 
         // Step 5: Runs in parallel
-        request.open_database(name, version);
+        if request.open_database(name, version).is_err() {
+            return Err(Error::Operation);
+        }
 
         // Step 6
         Ok(request)
@@ -81,7 +83,9 @@ impl IDBFactoryMethods<crate::DomTypeHolder> for IDBFactory {
         let request = IDBOpenDBRequest::new(&self.global(), CanGc::note());
 
         // Step 4: Runs in parallel
-        request.delete_database(name.to_string());
+        if request.delete_database(name.to_string()).is_err() {
+            return Err(Error::Operation);
+        }
 
         // Step 5: Return request
         Ok(request)

components/script/dom/idbopendbrequest.rs

@@ -224,7 +224,7 @@ impl IDBOpenDBRequest {
         self.idbrequest.set_error(error, can_gc);
     }
 
-    pub fn open_database(&self, name: DOMString, version: Option<u64>) {
+    pub fn open_database(&self, name: DOMString, version: Option<u64>) -> Result<(), ()> {
         let global = self.global();
 
         let (sender, receiver) = ipc::channel(global.time_profiler_chan().clone()).unwrap();
@@ -286,13 +286,17 @@ impl IDBOpenDBRequest {
             }),
         );
 
-        global
+        if global
             .resource_threads()
             .send(IndexedDBThreadMsg::Sync(open_operation))
-            .unwrap();
+            .is_err()
+        {
+            return Err(());
+        }
+        Ok(())
     }
 
-    pub fn delete_database(&self, name: String) {
+    pub fn delete_database(&self, name: String) -> Result<(), ()> {
         let global = self.global();
 
         let (sender, receiver) = ipc::channel(global.time_profiler_chan().clone()).unwrap();
@@ -317,10 +321,14 @@ impl IDBOpenDBRequest {
             }),
         );
 
-        global
+        if global
             .resource_threads()
             .send(IndexedDBThreadMsg::Sync(delete_operation))
-            .unwrap();
+            .is_err()
+        {
+            return Err(());
+        }
+        Ok(())
     }
 
     pub fn dispatch_success(&self, result: &IDBDatabase) {