Add a `kind` field to memory reports.

This is used for two memory reporting improvements.

- It's used to distinguish "explicit" memory reports from others. This
  mirrors the same categorization that is used in Firefox, and gives a single
  tree that's the best place to look. It replaces the "pages" tree which
  was always intended to be a temporary stand-in for "explicit".

- It's used to computed "heap-unclassified" values for both the jemalloc
  and system heaps, both of which are placed into the "explicit" tree.

Example output:
```
|  114.99 MiB -- explicit
|      52.34 MiB -- jemalloc-heap-unclassified
|      46.14 MiB -- system-heap-unclassified
|      14.95 MiB -- url(file:///home/njn/moz/servo2/../servo-static-suite/wikipe
dia/Guardians%20of%20the%20Galaxy%20(film)%20-%20Wikipedia,%20the%20free%20encyc
lopedia.html)
|          7.32 MiB -- js
|             3.07 MiB -- malloc-heap
|             3.00 MiB -- gc-heap
|                2.49 MiB -- used
|                0.34 MiB -- decommitted
|                0.09 MiB -- unused
|                0.09 MiB -- admin
|             1.25 MiB -- non-heap
|          1.36 MiB -- layout-worker-3-local-context
|          1.34 MiB -- layout-worker-0-local-context
|          1.24 MiB -- layout-worker-1-local-context
|          1.24 MiB -- layout-worker-4-local-context
|          1.16 MiB -- layout-worker-2-local-context
|          0.89 MiB -- layout-worker-5-local-context
|          0.38 MiB -- layout-task
|             0.31 MiB -- display-list
|             0.07 MiB -- local-context
|       1.56 MiB -- compositor-task
|          0.78 MiB -- surface-map
|          0.78 MiB -- layer-tree
```
The heap-unclassified values dominate the "explicit" tree because reporter
coverage is still quite poor.

1 files changed, 36 insertions, 10 deletions

diff --git a/components/script/script_task.rs b/components/script/script_task.rs
index d9560e40911..e34e93008d2 100644
--- a/components/script/script_task.rs
+++ b/components/script/script_task.rs
@@ -70,7 +70,7 @@ use net_traits::{ResourceTask, LoadConsumer, ControlMsg, Metadata};
 use net_traits::LoadData as NetLoadData;
 use net_traits::image_cache_task::{ImageCacheChan, ImageCacheTask, ImageCacheResult};
 use net_traits::storage_task::StorageTask;
-use profile_traits::mem::{self, Report, Reporter, ReporterRequest, ReportsChan};
+use profile_traits::mem::{self, Report, Reporter, ReporterRequest, ReportKind, ReportsChan};
 use string_cache::Atom;
 use util::str::DOMString;
 use util::task::spawn_named_with_send_on_failure;
@@ -1042,18 +1042,44 @@ impl ScriptTask {
             let rt = JS_GetRuntime(cx);
             let mut stats = ::std::mem::zeroed();
             if CollectServoSizes(rt, &mut stats) {
-                let mut report = |mut path_suffix, size| {
-                    let mut path = path!["pages", path_seg, "js"];
+                let mut report = |mut path_suffix, kind, size| {
+                    let mut path = path![path_seg, "js"];
                     path.append(&mut path_suffix);
-                    reports.push(Report { path: path, size: size as usize })
+                    reports.push(Report {
+                        path: path,
+                        kind: kind,
+                        size: size as usize,
+                    })
                 };
 
-                report(path!["gc-heap", "used"], stats.gcHeapUsed);
-                report(path!["gc-heap", "unused"], stats.gcHeapUnused);
-                report(path!["gc-heap", "admin"], stats.gcHeapAdmin);
-                report(path!["gc-heap", "decommitted"], stats.gcHeapDecommitted);
-                report(path!["malloc-heap"], stats.mallocHeap);
-                report(path!["non-heap"], stats.nonHeap);
+                // A note about possibly confusing terminology: the JS GC "heap" is allocated via
+                // mmap/VirtualAlloc, which means it's not on the malloc "heap", so we use
+                // `ExplicitNonHeapSize` as its kind.
+
+                report(path!["gc-heap", "used"],
+                       ReportKind::ExplicitNonHeapSize,
+                       stats.gcHeapUsed);
+
+                report(path!["gc-heap", "unused"],
+                       ReportKind::ExplicitNonHeapSize,
+                       stats.gcHeapUnused);
+
+                report(path!["gc-heap", "admin"],
+                       ReportKind::ExplicitNonHeapSize,
+                       stats.gcHeapAdmin);
+
+                report(path!["gc-heap", "decommitted"],
+                       ReportKind::ExplicitNonHeapSize,
+                       stats.gcHeapDecommitted);
+
+                // SpiderMonkey uses the system heap, not jemalloc.
+                report(path!["malloc-heap"],
+                       ReportKind::ExplicitSystemHeapSize,
+                       stats.mallocHeap);
+
+                report(path!["non-heap"],
+                       ReportKind::ExplicitNonHeapSize,
+                       stats.nonHeap);
             }
         }
         reports