Add an about:memory page (#35728)

This patch exposes a servo internal DOM API that is only made available to about:
pages on the navigator object to request memory reports. The about:memory page itself is
loaded like other html resources (eg. bad cert, net error) and makes use of this new API.

On the implementation side, notable changes:
- components/script/routed_promise.rs abstracts the setup used to fulfill a promise when the
  work needs to be routed through the constellation. The goal is to migrate other similar
  promise APIs in followup (eg. dom/webgpu/gpu.rs, bluetooth.rs).
- a new message is added to request a report from the memory reporter, and the memory reporter
  creates a json representation of the set of memory reports.
- the post-processing of memory reports is done in Javascript in the about-memory.html page,
  providing the same results as the current Rust code that outputs to stdout. We can decide
  later if we want to remove the current output.

Signed-off-by: webbeef <me@webbeef.org>

components/profile/mem.rs

@@ -15,7 +15,8 @@ use ipc_channel::ipc::{self, IpcReceiver};
 use ipc_channel::router::ROUTER;
 use parking_lot::{Condvar, Mutex};
 use profile_traits::mem::{
-    ProfilerChan, ProfilerMsg, ReportKind, Reporter, ReporterRequest, ReportsChan,
+    MemoryReportResult, ProfilerChan, ProfilerMsg, Report, ReportKind, Reporter, ReporterRequest,
+    ReportsChan,
 };
 use profile_traits::path;
 
@@ -143,10 +144,35 @@ impl Profiler {
                 true
             },
 
+            ProfilerMsg::Report(sender) => {
+                let reports = self.collect_reports();
+                let content = serde_json::to_string(&reports)
+                    .unwrap_or_else(|_| "{ error: \"failed to create memory report\"}".to_owned());
+                let _ = sender.send(MemoryReportResult { content });
+                // Notify the timer thread.
+                let (mutex, cvar) = &*self.notifier;
+                let mut done = mutex.lock();
+                *done = true;
+                cvar.notify_one();
+                true
+            },
+
             ProfilerMsg::Exit => false,
         }
     }
 
+    fn collect_reports(&self) -> Vec<Report> {
+        let mut result = vec![];
+        for reporter in self.reporters.values() {
+            let (chan, port) = ipc::channel().unwrap();
+            reporter.collect_reports(ReportsChan(chan));
+            if let Ok(mut reports) = port.recv() {
+                result.append(&mut reports);
+            }
+        }
+        result
+    }
+
     fn handle_print_msg(&self) {
         let elapsed = self.created.elapsed();
         println!("Begin memory reports {}", elapsed.as_secs());