Auto merge of #14312 - asajeffrey:script-discard-documents, r=cbrewster

Implement discarding Document objects to reclaim space.

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This PR implements document discarding. Active documents are kept alive strongly, but inactive documents are only kept alive weakly. When a document is GCd, it is marked as discarded, and if it is every reactivated, a reload of the URL is triggered.

Note that this PR is pretty aggressive about discarding, and can any inactive document (other than those being kept alive by other same-origin pipelines). We might want to damp it down a bit.

Also note that this interacts with browser.html in that the reloading triggered by reactivating a document triggers mozbrowser events.

To test this, I added a `-Zdiscard-inactive-documents` debug flag, which discards all inactive documents, even ones which are reachable through other same-origin pipelines.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #14262.
- [X] These changes do not require tests because we should be able to use the existing tests with `-Zdiscard-inactive-documents`.

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1 files changed, 6 insertions, 4 deletions

diff --git a/components/script/timers.rs b/components/script/timers.rs
index 14c4eb89c13..b86bdc17aae 100644
--- a/components/script/timers.rs
+++ b/components/script/timers.rs
@@ -228,18 +228,20 @@ impl OneshotTimers {
     }
 
     pub fn suspend(&self) {
-        assert!(self.suspended_since.get().is_none());
+        // Suspend is idempotent: do nothing if the timers are already suspended.
+        if self.suspended_since.get().is_some() {
+            return warn!("Suspending an already suspended timer.");
+        }
 
         self.suspended_since.set(Some(precise_time_ms()));
         self.invalidate_expected_event_id();
     }
 
     pub fn resume(&self) {
-        assert!(self.suspended_since.get().is_some());
-
+        // Suspend is idempotent: do nothing if the timers are already suspended.
         let additional_offset = match self.suspended_since.get() {
             Some(suspended_since) => precise_time_ms() - suspended_since,
-            None => panic!("Timers are not suspended.")
+            None => return warn!("Resuming an already resumed timer."),
         };
 
         self.suspension_offset.set(self.suspension_offset.get() + additional_offset);