Bug 1636266 - Report XUL Cache StyleSheet Memory r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D74450

dom/xul/nsXULPrototypeCache.cpp

@@ -504,7 +504,13 @@ void nsXULPrototypeCache::CollectMemoryReports(
   // TODO Report content in mPrototypeTable?
 
   other += sInstance->mStyleSheetTable.ShallowSizeOfExcludingThis(mallocSizeOf);
-  // TODO Report content inside mStyleSheetTable?
+  for (auto iter = sInstance->mStyleSheetTable.ConstIter(); !iter.Done();
+       iter.Next()) {
+    // NOTE: If Loader::DoSheetComplete() is ever modified to stop clongin
+    // sheets before inserting into this cache, we will need to stop using
+    // SizeOfIncludingThis()
+    other += iter.Data()->SizeOfIncludingThis(mallocSizeOf);
+  }
 
   other += sInstance->mScriptTable.ShallowSizeOfExcludingThis(mallocSizeOf);
   // TODO Report content inside mScriptTable?

layout/style/Loader.cpp

@@ -1856,6 +1856,10 @@ void Loader::DoSheetComplete(SheetLoadData& aLoadData,
           // We need to clone the sheet on insertion to the cache because
           // if the original sheet has a cyclic reference this can cause
           // leaks until shutdown since the global cache is not cycle-collected
+
+          // NOTE: If we stop cloning sheets before insertion, we need to change
+          // nsXULPrototypeCache::CollectMemoryReports() to stop using
+          // SizeOfIncludingThis() because it will no longer own the sheets.
           cache->PutStyleSheet(CloneSheet(*sheet));
         }
       }